Philip A. Rea, D.Phil. Professor of Biology D.Phil., University of Oxford, 1982 103D Carolyn Lynch Laboratory Department of Biology 433 South University Avenue University of Pennsylvania Philadelphia, PA 19104-6018 USA V +1 215 898.0807/8 F +1 215 898.8780 E parea@sas.upenn.edu

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external links: Life Sciences & Management - a new undergraduate program: http://www.upenn.edu/lsm.htm New Phytologist Symposium: http://www.newphytologist.org/heavymetals/ Genomics and Computational Biology Graduate Group: http://www.med.upenn.edu/gcb/ 60-Second Lecture on "Intracellular Landfills": http://www.sas.upenn.edu/home/news/sixtysec_lectures.html   energy-dependent transport and cellular detoxification processes Our research activities center on the molecular biology, cellular biochemistry and proteomics of vacuolar function with special emphasis on membrane transport proteins and the enzymic machinery responsible for the detoxification of xenobiotics, especially heavy metals. Long-term objectives are to identify the proteins concerned and elucidate their mechanisms of action and regulatory characteristics. The approach taken is that of the 'basic biologist' – the search for general principles, regardless of the organism in which they are to be gained, not just principles applicable to plants. Many of the investigations being conducted therefore entail parallel molecular and biochemical manipulations of several model systems including the plant Arabidopsis thaliana, the yeast Saccharomyces cerevisiae and the worm Caenorhabditis elegans. It is by this approach that we have been able to make fundamental contributions toward understanding a remarkably broad range of transport and related phenomena of general significance. a. ABC transporters The ATP-binding cassette (ABC) protein superfamily is one the largest protein families known, and most, but not all, are membrane proteins ("ABC transporters") active in the transport of a broad range of substances across membranes (Figure 1). Many of these proteins have been implicated in human diseases such as cystic fibrosis and Tangier disease, and resistance to therapies for cancer, malaria, and AIDS. To quote from Higgins (2001): The study of ABC transporters, in all their guises, has now become a minor industry. This is a far cry from ‘orphan’ beginnings, and provides a wonderful example of scientific serendipity, how fundamental studies of obscure model microbial processes, pretty much for their intrinsic interest with no obvious commercial or medical implications, can unexpectedly have a significant impact in unimagined arenas of biology. We have played a central role in the identification and molecular characterization of glutathione S-conjugate pumps (GS-X pumps) in yeast and plants. GS-X pumps, which belong to the multidrug resistance-associated protein (MRP) subfamily of ABC transporters, are involved in the vacuolar sequestration or plasma membrane extrusion and detoxification of both endogenous and exogenous toxins. Examples of substances transported by such membrane proteins are herbicides and heavy metals, such as cadmium and arsenic. As such, these transporters and their genes are of potential value for engineering plants with an increased capacity for the removal of toxic materials from contaminated soils (Rea et al – US Patent No. 6,166,299). Current research is concerned with the analysis of Arabidopsis T-DNA insertion mutants for some of these transporters and in extending our understanding of the general significance of ABC transporters for plants by examining the members of other subfamilies, including those implicated in the transport of sterols and lipids, and others implicated in the transport of iron-sulfur clusters across membranes for assembly of the prosthetic groups of oxidoreductases. The overall impact of this work is illustrated by the fact that Arabidopsis is unusual in its large allocation of open reading frames (a minimum of 0.5%) to members of the ABC protein superfamily. We have assembled a rigorous inventory of more than 130 ORFs for ABC proteins in Arabidopsis, of which more than 100 are transmembrane proteins. This gene count far outstrips those for the human genome and any other animal genome sequenced. figure 1 ATP-binding cassette (ABC) transporters are ubiquitous, with more than 3000 identified to date. A species or cell type ranging from the most primitive of microbes to man has yet to be discovered that lacks representatives of this superfamily. Bold as it may seem, it is conceivable that the in depth characterization of any biological process will necessitate an understanding of at least one ABC transporter (Holland et al 2003). The capabilities of ABC transporters are staggering and range from the transport of mineral ions to lipids and peptides through channel regulation to the regulation of other primary pumps. Reproduced from ABC Proteins: From Bacteria to Man, Ed. Holland et al (2003), which includes a chapter on the plant ABC transporter superfamily by Rea et al. b. phytochelatin-dependent heavy metal detoxification It has been known for some time that plants and some fungi synthesize peptides termed phytochelatins (PCs) from glutathione (GSH) when exposed to heavy metals. However, the molecular identity of the enzyme(s) responsible eluded definition until the first cloning of the enzyme PC synthase (AtPCS1) from Arabidopsis by ourselves and two other groups. The isolation of AtPCS1 and its demonstrated sufficiency for PC synthesis from GSH both in vitro and in vivo has enabled detailed mechanistic analyses of this enzyme and the provision of probes and methodologies for the identification and characterization of its orthologs in animals, as exemplified by our studies of C. elegans. In those systems that have been studied in sufficient detail, namely the fission yeast Schizosaccharomyces pombe and plants, PC thiols coordinate and chelate heavy metals to promote their removal from the cytosol by vacuolar sequestration. In the most thoroughly characterized of these systems, S. pombe, the vacuolar sequestration of heavy metal-PC complexes has been inferred to be catalyzed by a vacuolar membrane-localized "half-molecule" ABC transporter, SpHMT1 (S. pombe heavy metal tolerance factor 1). Molecular, biochemical and genetic studies of C. elegans demonstrate for the first time that PC-dependent heavy metal detoxification processes are also operative in some animals, not only at the level of PC synthase (CePCS-1) but also at the level of ABC transporter-catalyzed PC transport (CeHMT1). Our finding that CeHMT1-deficient worms, like CePCS1-deficient worms, are Cd2+-hypersensitive is consistent with the general applicability of such a scheme to other organisms that harbor genes for HMT1-type ABC transporters. figure 2 Synthesis of PC3 from GSH and PC2 by dipeptidyl transfer or tripeptidyl transfer. In dipeptidyl transfer, PC chain extension proceeds in the C to N direction and is not associated with the production of des(Gly)PCs, according to the general equation PCn + PCm = PCn+1 + PCm-1, where PC1 = GSH. In tripeptidyl transfer, PC chain extension proceeds in the N to C direction and is associated with the production of des(Gly)PCs according to the general equation PCn + PCm = PCn+1 + des(Gly)PCm+1 + G, where des(Gly)PC1 = γ-Glu-Cys. Also shown is a space-filling model of PC3 gray, white, red, blue, and yellow spheres denote C, H, O, N, and S atoms, respectively. Of these two schemes, the first, dipeptidyl transfer, applies to the reaction catalyzed by PC synthases. Reproduced from Rea et al (2004). Although studies of PC synthases have largely been concerned with the enzymes from eukaryotes, recent database searches have disclosed PC synthase-like sequences in the genomes of several prokaryotes. In and of itself, this finding might not be of particular interest except that all of the prokaryotic PC synthase homologs identified are half the length of their cognates from eukaryotes (220–237 residues compared with 421–506 residues) because they lack the more sequence-variable C-terminal domain (Figure 3). The one prokaryotic PC synthase homolog to have been assayed for activity, the alr0975 protein from the cyanobacterium Nostoc sp. PCC 7120 (NsPCS), catalyzes the deglycylation of GSH to γ-Glu-Cys at a high rate and the synthesis of PC2 at a relatively low rate (Figure 3). A recent crystal structure of NsPCS in its native and γ-Glu-Cys-acylated state (Vivares et al 2006) establishes, as had been inferred from our detailed kinetic, protein chemical, and site mutagenic analyses of the prototypical eukaryotic PC synthase, AtPCS1, that these enzymes belong to the papain superfamily and deploy a cysteine protease-like catalytic mechanism. While this crystal structure, the first for a PC synthase, was indeed seminal, it will be imperative to acquire structural information for eukaryotic PC synthases either as C-terminal truncates or full-length molecules. Toward this end, we have established that the N-terminal domain of AtPCS1 is sufficient for the Cd2+-dependent synthesis of PCs from GSH and undergoes Cd2+-independent γ-Glu-Cys acylation whereas the C-terminal domain is necessary for two processes that are not essential for core catalysis, augmentative free Cd2+ sensing and γ-Glu-Cys acylation of the full-length enzyme at a second site (Figure 3). figure 3 The catalytic bias of NsPCS favors the deglycylation of GSH to free γ-Glu-Cys (shown in black) over the N-terminal transpeptidation of GSH to generate PC2[(γ-Glu-Cys)2-Gly] (shown in gray); the converse applies to AtPCS1. The positions of the Cys residues are indicated by white vertical bars, and the conserved His and Asp residues are indicated by blue and red bars, respectively. AtPCS1 residues Cys-56, His-162, and Asp-180 are the three residues that are conserved in all known PC synthases and align with the catalytic residues of NsPCS, Cys-70, His-183, and Asp-201. NsPCS undergoes γ-Glu-Cys acylation at only one site; AtPCS1 undergoes acylation at two sites. The second site of acylation of full-length AtPCS1 is probably in the C-terminal domain (light gray), as is the site for direct interaction with and stimulation by free Cd2+. Reproduced from Rea (2006). When account is taken of the fact that in many plant species, PCs are the major ligands responsible for heavy metal accumulation and detoxification, AtPCS1 and genes like it may come to assume prominence in the development of phytoremediation technologies through genetic manipulation of the capacity of plants for heavy metal hyperaccumulation (Rea et al – US Patent No. 6,489,537). By the same token, the operation of equivalent metal detoxification pathways in nematodes and their cousins, some of which are pathogenic, may result in the development of new strategies for combating some of the many diseases caused by these organisms.   c. pyrophosphate-energized proton pumps Our studies have been instrumental in elucidating the basic organization and core catalytic capabilities of proton-translocating inorganic pyrophosphatases (V-PPases), a novel class of proton pump (Figure 4). Membrane-associated proton-translocating PPases are primary proton pumps that use inorganic pyrophosphate (PPi), the limiting case of a high energy phosphate, instead of ATP as an energy source for the establishment of transmembrane electrochemical potentials. Although the initial objective of these studies was to understand the mechanism of this pump in plants, recent investigations in our's and other laboratories have demonstrated these pumps in organisms as disparate as thermophilic Archaea and parasitic protists. Among the many evolutionary, practical and bioenergetic implications of these findings is the possibility that this research will spawn new approaches to the treatment of several prolific and debilitating parasite-mediated infections. Given our success in isolating knockout mutants for all three V-PPase genes in Arabidopsis, one type I gene and two type II genes, we are actively engaged in determining the physiological impact of this class of proton pump at the whole plant level. figure 4 Conservation of sequence and topology among V-PPases. A tentative topological model of AVP1 together with the five ‘toolbox’ sequences used for genome database searches and PCR are shown. Similar topologies have been predicted for the archaeal V-PPase, PVP and the bacterial PPi synthase, RVP. Open circles denote amino acid residues encompassed by the additional N-terminal transmembrane span predicted for AVP2. Roman numerals denote cytosolic loops. The peptide sequences against which polyclonal antibodies PABHK and PABTK used widely by the research community were raised are delimited by yellow bars. Reproduced from Drozdowicz and Rea (2001).   d. vacuolar proteomics Despite its large size and the numerous processes in which it is implicated, neither the full complement nor the functions of the proteins targeted to the yeast (Saccharomyces cerevisiae) vacuole have been defined comprehensively. To assist the research community in addressing this shortfall in our knowledge, we are building on the expertise and resources we have assembled for the purification of ‘proteomics-grade’ intact vacuoles, analysis of their membrane and luminal protein composition, and elucidation of the mode of uptake of a broad range of complex organic molecules to establish a methodological platform and protein inventory. This we are doing using the equipment we have recently installed in the Department of Biology: a robotic Micromass MassPREP station with enclosure for the in situ protease digestion of protein preparations or gel slices/plugs, and the preparation of samples for introduction into the MALDI-TOF-MS, a Micromass MALDI-TOF Reflectron MS instrument inclusive of high-end PCs and requisite software, and a liquid chromatography Q-Tof tandem MS (LCQ-MS). Using these ‘proteomics-grade’ intact vacuoles, 360 luminal polypeptide species have been resolved reproducibly by two-dimensional gel electrophoresis (Figure 5). Of these, 117 have been identified by MALDI-TOF MS and/or LCQ-MS through the deployment of ProteinLynx-, MASCOT- and/or SEQUEST-based protein sequence database searches in combination with Mr and pI considerations. The polypeptides identified, many of which correspond to alternate isoelectric and size states of the same parent translation product, can be assigned to 66 unique reading frames. In strict agreement with a predominantly lysosomal function for the yeast vacuole, most of the proteins identified are either canonical vacuolar proteases or proteins involved in intermediary metabolism, protein synthesis, folding or targeting, or the alleviation of oxidative stress that have entered this compartment for salvage purposes. The vacuole of S. cerevisiae, which can occupy as much as 25% of total intracellular volume, participates in numerous cellular processes ranging from macromolecule degradation and salvage, pH and general ion homeostasis, osmoregulation and volume regulation, the storage of amino acids, carboxylic acids, carbohydrates and some vitamins, to the sequestration of endogenous and exogenous toxins. What is perhaps surprising given this multifunctionality is how little is known of the range of proteins found in this compartment and the types of modifications to which they are subject. For instance, while protein turnover is one of the most thoroughly investigated functions of the yeast vacuole, and many of the proteins that participate have been known for some time, this and related processes have yet to be explored at the systems level through the application of global proteomics approaches. figure 5 2-DE separation of S. cerevisiae vacuolar lysate and MALDI-TOF-MS identification of carboxypeptidase Y and vacuolar aminopeptidase I, Ysc1p. For separation in the first dimension, yeast vacuolar lysate was loaded onto 11 cm immobilized pH 3-10 gradient (IPG) gel strips and isoelectric focused for 5.3 h at an integrated voltage of 30 kVh in a flat-bed Protean IEF cell (Bio-Rad). Separation in the second dimension was on 8-16% Criterion polyacrylamide gels (Bio-Rad). The protein spots were visualized with Bio-Safe Coomassie Blue. After excision, the stained gel plugs were in situ digested in a MassPREP station, mixed with matrix, spotted on a stainless steel MALDI target plate and subjected to Reflectron MALDI analysis (Chen, S., Collum, R.P., Peng, M., and Rea, P.A., unpublished data). A lack of systems level knowledge of the range of proteins to be found in this organelle could mean there are luminal proteins that remain to be discovered, which in turn might pose an impasse for the rational analysis of many cellular processes and ultimately cellular engineering. If vacuolate cells, for instance those of yeast, are to be manipulated for enhanced nutritional quality, for the provision of pharmaceuticals or their precursors, for the provision of precursors for manufacturing purposes, or for environmental remediation applications, it will by critical that the research community has ready access to a virtual vacuole (‘vacuomics’) toolbox detailing the protein profile of the vacuole lumen and how the latter is established and maintained by intravacuolar reactions and transport across the vacuolar membrane. S. cerevisiae possesses only a moderate number of open reading frames, most of which are devoid of introns, and as one of the most molecularly manipulable genomically characterized eukaryotes, is a model system for the identification and definition of eukaryotic protein functions. Moreover, since it is vacuolate and the core machinery for protein delivery into and processing within the vacuole is likely conserved in other vacuolysosomal structures, investigations of S. cerevisiae have the potential to contribute to our understanding of not only other fungal systems and plants but also the lysosomal compartments of animal cells. Although we know that exogenous heavy metals such as cadmium are chelated by thiol peptides and imported into the vacuole for sequestration, much less is known about the downstream processing of thiols after they enter the vacuole, the enzymes involved in this processing, and the long term storage of heavy metals after sequestration. Having established a methodological platform for analyzing the vacuolar luminal proteome of S. cerevisiae, current studies are directed towards determining the proteomic and metabolomic effects of cadmium on the vacuolar luminal profile of wild-type S. cerevisiae and mutants harboring a deletion in the ycf1 (yeast cadmium factor 1) gene that encodes the principal vacuolar ABC transporter responsible for catalyzing MgATP-dependent uptake of Cd-glutathione complexes into this compartment, a collaboration with Christophe Junot at the Commissariat à l'Energie Atomique (CEA), Saclay, France who is taking the lead in the LC-MS based identification and quantitation of vacuolar thiols and their derivatives. Roy and Diana Vagelos Program in Life Sciences & Management The Life Sciences and Management program (LSM) is a new joint effort of the College of Arts & Sciences and the Wharton School that combines extensive coursework in both the life sciences and management in preparation for intellectually and managerially challenging careers in for-profit and non-profit, private and public organizations in the rapidly growing life sciences sector. This program aims to meet the need for students seeking a leadership career in science to have a firm understanding of management, to venture into the realm of decision making with the ability to communicate science transparently, and for those planning management careers in the life sciences to have a deep understanding of science and, even more importantly, experience with the processes of discovery and development in the laboratory. Participants pursue a curriculum that allows them to understand and to discuss the foundations and prospects for science, as well as develop skills in strategic marketing, product development and management, and public policy. figure 6 A key feature of the LSM curriculum is the practical experience students get outside the classroom. Each student enrolled in the program completes two paid summer internships - a business internship after the sophomore year, followed by a scientific research internship after the junior year. These internships can take place in a variety of settings, including pharmaceutical or agrochemical corporations, biotechnological startup companies, government laboratories, academic research centers, and consulting and investment firms. In their senior year, students take their business and laboratory experiences one step further through a capstone course, for which they develop a business plan and management strategy for their own scientific project. The capstone brings the learning experience full-circle, allowing students to merge their scientific and business knowledge while incorporating real-life situations into the academic curriculum. Our research at the interface between the life sciences and their implementation focuses on case studies that highlight the difficult transition from discovery in the laboratory to success in the market. Modules that we are currently developing include “From the obscure to the billion dollar pill; from the obvious but undoable to the done and obstructed: statins and Golden Rice” and “Seeing red and green – the FlavrSavr tomato and the quiet Green Revolution.”

selected publications Raichaudhuri, A., Peng, M., Naponelli, V., Chen, S., Sánchez-Fernández, R., Gu, H., Gregory III, J.F., Hanson, A.D., Rea, P.A. (2009) Plant vacuolar ABC transporters that translocate folates and antifolates in vitro and contribute to antifolate tolerance in vivo. J. Biol. Chem., in press. Sooksa-nguan, T., Yakubov, B., Kozlovskyy, V.I., Barkume, C.M., Howe, K.J., Thannhauser, T.W., Rutzke, M.A., Hart, J.J., Kochian, K.V., Rea, P.A., Vatamaniuk, O.K. (2009) Drosophila ABC transporter, DmHMT-1, confers tolerance to cadmium.  DmHMT-1 and its yeast homolog, SpHMT-1, are not essential for vacuolar phytochelatin sequestration. J. Biol. Chem., 284: in press. Rea, P.A. (2008) Statins: from fungus to pharma. Am. Sci., 96: 408-415. Verrier, P.J., Bird, D., Burla, B., Dassa, E., Forestier, C., Geisler, M., Klein, M., Kolukisaoglu, U., Lee, Y., Martinoia, E., Murphy, A., Rea, P.A., Samuels, L., Schulz, B., Spalding, E., Yazaki, K., Theodoulou, F.L. (2008) Plant ABC proteins – a unified nomenclature and updated inventory.  Trends Plant Sci., 13: 151-159. Sarry, J.-E., Chen, S., Collum, R.P., Liang, S., Peng, M., Lang, A., Naumann, B., Dzierszinski, F., Yuan, C.-X., Hippler, M., Rea, P.A. (2007) Analysis of the vacuolar luminal proteome of Saccharomyces cerevisiae. FEBS J., 274: 4287-4305. Chen, S., Sánchez-Fernández, R., Lyver, E.R., Dancis, A., Rea. P.A. (2007) Functional characterization of AtATM1, AtATM2 and AtATM3, a subfamily of Arabidopsis half-molecule ABC transporters implicated in iron homeostasis. J. Biol. Chem., 282: 21561-21571. Rea, P.A. (2007) Plant ATP-binding cassette transporters. Annu. Rev. Plant Biol., 58: 347-375. Romanyuk, N.D., Rigden, D.J., Vatamaniuk, O.K., Lang, A., Cahoon, R.E., Jez, J.M., Rea, P.A. (2006) Mutagenic definition of papain-like catalytic triad, sufficiency of N-terminal domain for single-site core catalytic enzyme acylation and C-terminal domain for augmentative metal activation of an eukaryotic phytochelatin synthase. Plant Physiol., 141:858-869. Rea, P.A. (2006) Phytochelatin synthase, papain's cousin, in stereo. Proc. Natl. Acad. Sci. USA, 103: 507-508. Rea, P.A. (2005) A farewell to bacterial ARMs? Nature Biotechnol.,23: 1085-1087. Orsomando, G., Diaz de la Garza, R., Green, B.J., Peng, M., Rea, P.A., Ryan, T.J., Gregory, J.F., Hanson, A.D. (2005) Plant γ-glutamyl hydrolases and folate polyglutamates. Characterization, compartmentation and co-occurrence in vacuoles. J. Biol. Chem., 280: 28877-28884. Vatamaniuk, O.K., Bucher, E.A., Sundaram, M.V., Rea, P.A. (2005) CeHMT-1, a putative phytochelatin transporter, is required for cadmium tolerance in Caenorhabditis elegans. J. Biol. Chem., 280: 23684-23690. Fall (2004) Photographs by Christopher Griffith, Verse by Walt Whitman, Text by Philip A. Rea. Hardcover, 11.25 x 14.25 inches, 80 pages, 48 four-color photographs. Powerhouse Publishers, New York. ISBN 1-57687-226-2. Rea, P.A., Vatamaniuk, O.K., Rigden, D.J. (2004) Weeds, worms and more: papain's long-lost cousin, phytochelatin synthase. Plant Physiol., 136: 2463-2474. Vatamaniuk, O.K., Mari, S., Lang, A., Chalasani, S., Demkiv, L.O., Rea, P.A. (2004) Phytochelatin synthase, a dipeptidyl transferase that undergoes multisite acylation with γ-glutamylcysteine during catalysis. Stoichiometric and site-directed mutagenic analysis of AtPCS1-catalyzed phytochelatin synthesis. J. Biol. Chem., 279: 22449-22460. Rea, P.A. (2003) Ion Genomics. Natural Biotechnol., 21: 1149-1151. Maathuis, F.J.M., Filatov, V., Krijger, G.C., Herzyk, P., Axelsen, K.B., Chen, S., Green, B.J., Madagan, K.L., Sánchez-Fernández, R., Forde, B., Palmgren, M.G., Rea, P.A., Williams, L.E., Sanders, D., Amtmann, A. (2003) Transcriptome analysis of Arabidopsis thaliana cation transport. Plant J., 65, 675-692. Rea, P.A., Sánchez-Fernández, R., Chen, S., Peng, M., Klein, M., Geisler, M., Martinoia, M. (2003) The plant ABC transporter superfamily: the functions of a few and the identities of many. In: ABC Transporters from Bacteria to Humans, (Cole, S.P., Kuchler, K., Higgins, C, Holland, B., eds), Academic Press, UK, pp. 335-356. Drozdowicz, Y.M., Shaw, M., Nishi, M., Striepen, B., Liwinski, H.A., Roos, D.S., and Rea, P.A. (2003) Isolation and characterization of TgVP1, a type I vacuolar proton translocating pyrophosphatase from Toxoplasma gondii: the dynamics of its subcellular localization and the cellular effects of a diphosphonate. J. Biol. Chem., 278: 1075-1085. Bartholomew, D.M., Van Dyk, D.E., Lau, S.-M., O'Keefe, D.P., Rea, P.A., and Viitanen, P.V. (2002) Alternate energy-dependent pathways for the vacuolar uptake of glucose and glutathione conjugates. High sensitivity, high fidelity transport measurements by LC-MS. Plant Physiol., 103: 1562-1572 Vatamaniuk, O.K., Bucher, E.A., and Rea, P.A. (2002) Worms take the 'phyto' out of 'phytochelatins'. Trends Biotechnol., 20: 61-64 Sánchez-Fernández, R., Davies, T.G.E., Coleman, J.O.D., and Rea, P.A. (2001) The Arabidopsis thaliana ABC protein superfamily: a complete inventory. J. Biol. Chem., 276: 30231-30244 Vatamaniuk, O.K., Bucher, E.A., Ward, J.T., and Rea, P.A. (2001) A new pathway for heavy metal detoxification in animals: phytochelatin synthase is required for cadmium tolerance in Caenorhabditis elegans. J. Biol. Chem., 276: 20817-20820 Drozdowicz, Y.M., and Rea, P.A. (2001) Vacuolar proton-pyrophosphatases: from the evolutionary backwaters into the mainstream. Trends Plant Sci., 6: 206-211 Liu, G., Sánchez-Fernández, R., and Rea, P.A. (2001) Enhanced multispecificity of vacuolar membrane-localized ABC transporter AtMRP2. J. Biol. Chem., 276: 8648-8656 Vatamaniuk, O.K., Mari, S., Lu, Y.-P., and Rea, P.A. (2000) Mechanism of heavy metal activation of phytochelatin (PC) synthase: blocked thiols are sufficient for PC synthase-catalyzed transpeptidation of glutathione and related thiol peptides. J. Biol. Chem., 275: 31451-31459 Drozdowicz, Y.M., Kissinger, J.C., and Rea, P.A. (2000) AVP2, a sequence-divergent, monovalent cation-insensitive proton-translocating inorganic pyrophosphatase from Arabidopsis thaliana. Plant Physiol., 123: 353-362 Drozdowicz, Y.M., Lu, Y.-P., Patel, V., Fitz-Gibbon, S., Miller, J., and Rea, P.A. (1999) PVP, a thermostable vacuolar-type pyrophosphate-dependent pump from the archaeon Pyrobaculum aerophilum: implications for the origins of pyrophosphate-energized pumps. FEBS Lett., 460: 505-512 Vatamaniuk, O.K., Mari, S., Lu, Y.-P., and Rea, P.A. (1999) AtPCS1, a phytochelatin synthase from Arabidopsis: isolation and in vitro reconstitution. Proc. Natl. Acad. Sci. USA., 96: 7110-7115 Rea, P.A. (1999) MRP subfamily ABC transporters from plants and yeast. J. Exp. Bot., 50: 895-913 Rea, P.A., Li, Z.-S., Lu, Y.-P., Drozdowicz, Y.M., and Martinoia, E. (1998) From vacuolar GS-X pumps to multispecific ABC transporters. Annu. Rev. Plant Physiol. Plant Mol. Biol., 49: 727-760 Lu, Y.-P., Li, Z.-S., Drozdowicz, Y.M., Hortensteiner, S., Martinoia, E., and Rea, P.A. (1998) AtMRP2, an Arabidopsis ATP-binding cassette transporter able to transport glutathione S-conjugates and chlorophyll catabolites: functional comparisons with AtMRP1. Plant Cell, 10: 1-18 Zhen, R.-G., Kim, E.J., and Rea, P.A. (1997) Acidic residues necessary for pyrophosphate-energized pumping and inhibition of the vacuolar proton-pyrophosphatase by N,N'-dicyclohexylcarbodiimide. J. Biol. Chem., 272: 22340-22348 Lu, Y.-P., Li, Z.-S., and Rea, P.A. (1997) AtMRP1 gene of A. thaliana encodes a glutathione S-conjugate pump: Isolation and functional definition of a plant ATP binding cassette transporter gene. Proc. Natl. Acad. Sci. USA, 94: 8243-8248 Li, Z.-S., Lu, Y.-P., Thiele, D.J., and Rea, P.A. (1997) A new pathway for vacuolar cadmium sequestration in Saccharomyces cerevisiae: YCF1-mediated transport of bis(glutathionato)cadmium. Proc. Natl. Acad. Sci. USA, 94: 42-47 Zhen, R.-G., Kim, E.J., and Rea, P.A. (1997) The molecular and biochemical basis of pyrophosphate-energized proton translocation at the vacuolar membrane. Adv. Bot. Res., 25: 297-337.   teaching BIOL 121, Molecular Biology of Life BIOL 402, Biochemistry LSMP 121, Proseminar in Management & The Life Sciences   current research group Richard Collum (rcollum@sas.upenn.edu) Dr. Ayan Raichaudhuri (ayanra@sas.upenn.edu) Albert Lang (alang@sas.upenn.edu) Dr. Philip A. Rea (parea@sas.upenn.edu) Dr. Jean-Emmanuel Sarry (jesarry@sas.upenn.edu) Tom Xu (tao@sas.upenn.edu)