1
|
Fietze T, Wilk P, Kabinger F, Anoosheh S, Hofer A, Lundin D, Feiler CG, Weiss MS, Loderer C. HUG Domain Is Responsible for Active Dimer Stabilization in an NrdJd Ribonucleotide Reductase. Biochemistry 2022; 61:1633-1641. [PMID: 35856337 DOI: 10.1021/acs.biochem.2c00173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to the corresponding deoxyribonucleotides. The catalytic activity of most RNRs depends on the formation of a dimer of the catalytic subunits. The active site is located at the interface, and part of the substrate binding site and regulatory mechanisms work across the subunit in the dimer. In this study, we describe and characterize a novel domain responsible for forming the catalytic dimer in several class II RNRs. The 3D structure of the class II RNR from Rhodobacter sphaeroides reveals a so far undescribed α-helical domain in the dimer interface, which is embracing the other subunit. Genetic removal of this HUG domain leads to a severe reduction of activity paired with reduced dimerization capability. In comparison with other described RNRs, the enzyme with this domain is less dependent on the presence of nucleotides to act as allosteric effectors in the formation of dimers. The HUG domain appears to serve as an interlock to keep the dimer intact and functional even at low enzyme and/or effector concentrations.
Collapse
Affiliation(s)
- Tobias Fietze
- Chair of Molecular Biotechnology, Technische Universität Dresden, Dresden 01217, Germany
| | - Piotr Wilk
- Macromolecular Crystallography, Helmholtz-Zentrum Berlin, Berlin 12489, Germany.,Malopolska Centre of Biotechnology (MCB), Jagiellonian University, Krakow 31-007, Poland
| | - Florian Kabinger
- Department of Molecular Biology, Max Planck Institute for Multidisciplinary Sciences, Göttingen 37077, Germany
| | - Saber Anoosheh
- Department of Medical Biochemistry, Umeå University, Umeå 1965, Sweden
| | - Anders Hofer
- Department of Medical Biochemistry, Umeå University, Umeå 1965, Sweden
| | - Daniel Lundin
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm 114 19, Sweden
| | - Christian G Feiler
- Macromolecular Crystallography, Helmholtz-Zentrum Berlin, Berlin 12489, Germany
| | - Manfred S Weiss
- Macromolecular Crystallography, Helmholtz-Zentrum Berlin, Berlin 12489, Germany
| | - Christoph Loderer
- Chair of Molecular Biotechnology, Technische Universität Dresden, Dresden 01217, Germany
| |
Collapse
|
2
|
Box-shaped ribozyme octamer formed by face-to-face dimerization of a pair of square-shaped ribozyme tetramers. J Biosci Bioeng 2022; 134:195-202. [PMID: 35810135 DOI: 10.1016/j.jbiosc.2022.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 06/14/2022] [Accepted: 06/14/2022] [Indexed: 11/21/2022]
Abstract
Naturally occurring ribozymes with defined three-dimensional (3D) structures serve as promising platforms for the design and construction of artificial RNA nanostructures. We constructed a hexameric ribozyme nanostructure by face-to-face dimerization of a pair of triangular ribozyme trimers, unit RNAs of which were derived from the Tetrahymena group I ribozyme. In this study, we have expanded the dimerization strategy to a square-shaped ribozyme tetramer by introducing four pillar units. The resulting box-shaped nanostructures, which contained eight ribozyme units, can be assembled from either four or two components of their unit RNAs.
Collapse
|
3
|
Long MJC, Ly P, Aye Y. Still no Rest for the Reductases: Ribonucleotide Reductase (RNR) Structure and Function: An Update. Subcell Biochem 2022; 99:155-197. [PMID: 36151376 DOI: 10.1007/978-3-031-00793-4_5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Herein we present a multidisciplinary discussion of ribonucleotide reductase (RNR), the essential enzyme uniquely responsible for conversion of ribonucleotides to deoxyribonucleotides. This chapter primarily presents an overview of this multifaceted and complex enzyme, covering RNR's role in enzymology, biochemistry, medicinal chemistry, and cell biology. It further focuses on RNR from mammals, whose interesting and often conflicting roles in health and disease are coming more into focus. We present pitfalls that we think have not always been dealt with by researchers in each area and further seek to unite some of the field-specific observations surrounding this enzyme. Our work is thus not intended to cover any one topic in extreme detail, but rather give what we consider to be the necessary broad grounding to understand this critical enzyme holistically. Although this is an approach we have advocated in many different areas of scientific research, there is arguably no other single enzyme that embodies the need for such broad study than RNR. Thus, we submit that RNR itself is a paradigm of interdisciplinary research that is of interest from the perspective of the generalist and the specialist alike. We hope that the discussions herein will thus be helpful to not only those wanting to tackle RNR-specific problems, but also those working on similar interdisciplinary projects centering around other enzymes.
Collapse
Affiliation(s)
- Marcus J C Long
- University of Lausanne (UNIL), Lausanne, Switzerland
- Department of Biochemistry, UNIL, Epalinges, Switzerland
| | - Phillippe Ly
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland
- EPFL SB ISIC LEAGO, Lausanne, Switzerland
| | - Yimon Aye
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland.
- EPFL SB ISIC LEAGO, Lausanne, Switzerland.
| |
Collapse
|
4
|
SAMHD1 Functions and Human Diseases. Viruses 2020; 12:v12040382. [PMID: 32244340 PMCID: PMC7232136 DOI: 10.3390/v12040382] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 03/27/2020] [Accepted: 03/28/2020] [Indexed: 12/12/2022] Open
Abstract
Deoxynucleoside triphosphate (dNTP) molecules are essential for the replication and maintenance of genomic information in both cells and a variety of viral pathogens. While the process of dNTP biosynthesis by cellular enzymes, such as ribonucleotide reductase (RNR) and thymidine kinase (TK), has been extensively investigated, a negative regulatory mechanism of dNTP pools was recently found to involve sterile alpha motif (SAM) domain and histidine-aspartate (HD) domain-containing protein 1, SAMHD1. When active, dNTP triphosphohydrolase activity of SAMHD1 degrades dNTPs into their 2'-deoxynucleoside (dN) and triphosphate subparts, steadily depleting intercellular dNTP pools. The differential expression levels and activation states of SAMHD1 in various cell types contributes to unique dNTP pools that either aid (i.e., dividing T cells) or restrict (i.e., nondividing macrophages) viral replication that consumes cellular dNTPs. Genetic mutations in SAMHD1 induce a rare inflammatory encephalopathy called Aicardi-Goutières syndrome (AGS), which phenotypically resembles viral infection. Recent publications have identified diverse roles for SAMHD1 in double-stranded break repair, genome stability, and the replication stress response through interferon signaling. Finally, a series of SAMHD1 mutations were also reported in various cancer cell types while why SAMHD1 is mutated in these cancer cells remains to investigated. Here, we reviewed a series of studies that have begun illuminating the highly diverse roles of SAMHD1 in virology, immunology, and cancer biology.
Collapse
|
5
|
Long MJC, Zhao Y, Aye Y. Clofarabine Commandeers the RNR-α-ZRANB3 Nuclear Signaling Axis. Cell Chem Biol 2019; 27:122-133.e5. [PMID: 31836351 DOI: 10.1016/j.chembiol.2019.11.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 08/30/2019] [Accepted: 11/19/2019] [Indexed: 02/08/2023]
Abstract
Ribonucleotide reductase (RNR) is an essential enzyme in DNA biogenesis and a target of several chemotherapeutics. Here, we investigate how anti-leukemic drugs (e.g., clofarabine [ClF]) that target one of the two subunits of RNR, RNR-α, affect non-canonical RNR-α functions. We discovered that these clinically approved RNR-inhibiting dATP-analogs inhibit growth by also targeting ZRANB3-a recently identified DNA synthesis promoter and nuclear-localized interactor of RNR-α. Remarkably, in early time points following drug treatment, ZRANB3 targeting accounted for most of the drug-induced DNA synthesis suppression and multiple cell types featuring ZRANB3 knockout/knockdown were resistant to these drugs. In addition, ZRANB3 plays a major role in regulating tumor invasion and H-rasG12V-promoted transformation in a manner dependent on the recently discovered interactome of RNR-α involving select cytosolic-/nuclear-localized protein players. The H-rasG12V-promoted transformation-which we show requires ZRANB3-supported DNA synthesis-was efficiently suppressed by ClF. Such overlooked mechanisms of action of approved drugs and a previously unappreciated example of non-oncogene addiction, which is suppressed by RNR-α, may advance cancer interventions.
Collapse
Affiliation(s)
- Marcus J C Long
- Bishop Burton, Beverley, East Riding of Yorkshire HU17 8QH, UK
| | - Yi Zhao
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Yimon Aye
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne 1015, Switzerland.
| |
Collapse
|
6
|
Long MJC, Van Hall-Beauvais A, Aye Y. The more the merrier: how homo-oligomerization alters the interactome and function of ribonucleotide reductase. Curr Opin Chem Biol 2019; 54:10-18. [PMID: 31734537 DOI: 10.1016/j.cbpa.2019.09.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 09/03/2019] [Accepted: 09/19/2019] [Indexed: 02/05/2023]
Abstract
Stereotyped as a nexus of dNTP synthesis, the dual-subunit enzyme - ribonucleotide reductase (RNR) - is coming into view as a paradigm of oligomerization and moonlighting behavior. In the present issue of 'omics', we discuss what makes the larger subunit of this enzyme (RNR-α) so interesting, highlighting its emerging cellular interactome based on its unique oligomeric dynamism that dictates its compartment-specific occupations. Linking the history of the field with the multivariable nature of this exceedingly sophisticated enzyme, we further discuss implications of new data pertaining to DNA-damage response, S-phase checkpoints, and ultimately tumor suppression. We hereby hope to provide ideas for those interested in these fields and exemplify conceptual frameworks and tools that are useful to study RNR's broader roles in biology.
Collapse
Affiliation(s)
| | - Alexandra Van Hall-Beauvais
- Swiss Federal Institute of Technology Lausanne (EPFL), Institute of Chemical Sciences and Engineering, 1015, Lausanne, Switzerland
| | - Yimon Aye
- Swiss Federal Institute of Technology Lausanne (EPFL), Institute of Chemical Sciences and Engineering, 1015, Lausanne, Switzerland.
| |
Collapse
|
7
|
Fu Y, Long MJC, Wisitpitthaya S, Inayat H, Pierpont TM, Elsaid IM, Bloom JC, Ortega J, Weiss RS, Aye Y. Nuclear RNR-α antagonizes cell proliferation by directly inhibiting ZRANB3. Nat Chem Biol 2018; 14:943-954. [PMID: 30150681 DOI: 10.1038/s41589-018-0113-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Accepted: 06/28/2018] [Indexed: 11/09/2022]
Abstract
Since the origins of DNA-based life, the enzyme ribonucleotide reductase (RNR) has spurred proliferation because of its rate-limiting role in de novo deoxynucleoside-triphosphate (dNTP) biosynthesis. Paradoxically, the large subunit, RNR-α, of this obligatory two-component complex in mammals plays a context-specific antiproliferative role. There is little explanation for this dichotomy. Here, we show that RNR-α has a previously unrecognized DNA-replication inhibition function, leading to growth retardation. This underappreciated biological activity functions in the nucleus, where RNR-α interacts with ZRANB3. This process suppresses ZRANB3's function in unstressed cells, which we show to promote DNA synthesis. This nonreductase function of RNR-α is promoted by RNR-α hexamerization-induced by a natural and synthetic nucleotide of dA/ClF/CLA/FLU-which elicits rapid RNR-α nuclear import. The newly discovered nuclear signaling axis is a primary defense against elevated or imbalanced dNTP pools that can exert mutagenic effects irrespective of the cell cycle.
Collapse
Affiliation(s)
- Yuan Fu
- Department of Chemistry & Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Marcus J C Long
- Department of Chemistry & Chemical Biology, Cornell University, Ithaca, NY, USA
| | | | - Huma Inayat
- Department of Anatomy and Cell Biology, McGill University, Montreal, QC, Canada
| | | | - Islam M Elsaid
- Department of Chemistry & Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Jordana C Bloom
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| | - Joaquin Ortega
- Department of Anatomy and Cell Biology, McGill University, Montreal, QC, Canada
| | - Robert S Weiss
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| | - Yimon Aye
- Ecole Polytechnique Fédérale de Lausanne, Institute of Chemical Sciences and Engineering, Lausanne, Switzerland.
| |
Collapse
|
8
|
Wisitpitthaya S, Zhao Y, Long MJC, Li M, Fletcher EA, Blessing WA, Weiss RS, Aye Y. Cladribine and Fludarabine Nucleotides Induce Distinct Hexamers Defining a Common Mode of Reversible RNR Inhibition. ACS Chem Biol 2016; 11:2021-32. [PMID: 27159113 DOI: 10.1021/acschembio.6b00303] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The enzyme ribonucleotide reductase (RNR) is a major target of anticancer drugs. Until recently, suicide inactivation in which synthetic substrate analogs (nucleoside diphosphates) irreversibly inactivate the RNR-α2β2 heterodimeric complex was the only clinically proven inhibition pathway. For instance, this mechanism is deployed by the multifactorial anticancer agent gemcitabine diphosphate. Recently reversible targeting of RNR-α-alone coupled with ligand-induced RNR-α-persistent hexamerization has emerged to be of clinical significance. To date, clofarabine nucleotides are the only known example of this mechanism. Herein, chemoenzymatic syntheses of the active forms of two other drugs, phosphorylated cladribine (ClA) and fludarabine (FlU), allow us to establish that reversible inhibition is common to numerous drugs in clinical use. Enzyme inhibition and fluorescence anisotropy assays show that the di- and triphosphates of the two nucleosides function as reversible (i.e., nonmechanism-based) inhibitors of RNR and interact with the catalytic (C site) and the allosteric activity (A site) sites of RNR-α, respectively. Gel filtration, protease digestion, and FRET assays demonstrate that inhibition is coupled with formation of conformationally diverse hexamers. Studies in 293T cells capable of selectively inducing either wild-type or oligomerization-defective mutant RNR-α overexpression delineate the central role of RNR-α oligomerization in drug activity, and highlight a potential resistance mechanism to these drugs. These data set the stage for new interventions targeting RNR oligomeric regulation.
Collapse
Affiliation(s)
- Somsinee Wisitpitthaya
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Yi Zhao
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Marcus J. C. Long
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Minxing Li
- Department
of Biomedical Sciences, Cornell University, Ithaca, New York 14853, United States
| | - Elaine A. Fletcher
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - William A. Blessing
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Robert S. Weiss
- Department
of Biomedical Sciences, Cornell University, Ithaca, New York 14853, United States
| | - Yimon Aye
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
- Department
of Biochemistry, Weill Cornell Medicine, New York, New York 10065, United States
| |
Collapse
|
9
|
Livada J, Martinie RJ, Dassama LMK, Krebs C, Bollinger JM, Silakov A. Direct Measurement of the Radical Translocation Distance in the Class I Ribonucleotide Reductase from Chlamydia trachomatis. J Phys Chem B 2015; 119:13777-84. [PMID: 26087051 DOI: 10.1021/acs.jpcb.5b04067] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ribonucleotide reductases (RNRs) catalyze conversion of ribonucleotides to deoxyribonucleotides in all organisms via a free-radical mechanism that is essentially conserved. In class I RNRs, the reaction is initiated and terminated by radical translocation (RT) between the α and β subunits. In the class Ic RNR from Chlamydia trachomatis (Ct RNR), the initiating event converts the active S = 1 Mn(IV)/Fe(III) cofactor to the S = 1/2 Mn(III)/Fe(III) "RT-product" form in the β subunit and generates a cysteinyl radical in the α active site. The radical can be trapped via the well-described decomposition reaction of the mechanism-based inactivator, 2'-azido-2'-deoxyuridine-5'-diphosphate, resulting in the generation of a long-lived, nitrogen-centered radical (N(•)) in α. In this work, we have determined the distance between the Mn(III)/Fe(III) cofactor in β and N(•) in α to be 43 ± 1 Å by using double electron-electron resonance experiments. This study provides the first structural data on the Ct RNR holoenzyme complex and the first direct experimental measurement of the inter-subunit RT distance in any class I RNR.
Collapse
Affiliation(s)
- Jovan Livada
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Ryan J Martinie
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Laura M K Dassama
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Carsten Krebs
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - J Martin Bollinger
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Alexey Silakov
- Departments of †Chemistry and ‡Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| |
Collapse
|
10
|
Fu Y, Lin H, Wisitpitthaya S, Blessing WA, Aye Y. A fluorimetric readout reporting the kinetics of nucleotide-induced human ribonucleotide reductase oligomerization. Chembiochem 2014; 15:2598-2604. [PMID: 25256246 DOI: 10.1002/cbic.201402368] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Indexed: 11/11/2022]
Abstract
Human ribonucleotide reductase (hRNR) is a target of nucleotide chemotherapeutics in clinical use. The nucleotide-induced oligomeric regulation of hRNR subunit α is increasingly being recognized as an innate and drug-relevant mechanism for enzyme activity modulation. In the presence of negative feedback inhibitor dATP and leukemia drug clofarabine nucleotides, hRNR-α assembles into catalytically inert hexameric complexes, whereas nucleotide effectors that govern substrate specificity typically trigger α-dimerization. Currently, both knowledge of and tools to interrogate the oligomeric assembly pathway of RNR in any species in real time are lacking. We therefore developed a fluorimetric assay that reliably reports on oligomeric state changes of α with high sensitivity. The oligomerization-directed fluorescence quenching of hRNR-α, covalently labeled with two fluorophores, allows for direct readout of hRNR dimeric and hexameric states. We applied the newly developed platform to reveal the timescales of α self-assembly, driven by the feedback regulator dATP. This information is currently unavailable, despite the pharmaceutical relevance of hRNR oligomeric regulation.
Collapse
Affiliation(s)
- Yuan Fu
- Department of Chemistry and Chemical Biology Cornell University, Ithaca, NY 14853
| | - Hongyu Lin
- Department of Chemistry and Chemical Biology Cornell University, Ithaca, NY 14853
| | | | - William A Blessing
- Department of Chemistry and Chemical Biology Cornell University, Ithaca, NY 14853
| | - Yimon Aye
- Department of Chemistry and Chemical Biology Cornell University, Ithaca, NY 14853.,Department of Biochemistry Weill Cornell Medical College, New York, NY, 10065
| |
Collapse
|
11
|
Aye Y, Li M, Long MJC, Weiss RS. Ribonucleotide reductase and cancer: biological mechanisms and targeted therapies. Oncogene 2014; 34:2011-21. [PMID: 24909171 DOI: 10.1038/onc.2014.155] [Citation(s) in RCA: 276] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 04/25/2014] [Accepted: 04/26/2014] [Indexed: 12/16/2022]
Abstract
Accurate DNA replication and repair is essential for proper development, growth and tumor-free survival in all multicellular organisms. A key requirement for the maintenance of genomic integrity is the availability of adequate and balanced pools of deoxyribonucleoside triphosphates (dNTPs), the building blocks of DNA. Notably, dNTP pool alterations lead to genomic instability and have been linked to multiple human diseases, including mitochondrial disorders, susceptibility to viral infection and cancer. In this review, we discuss how a key regulator of dNTP biosynthesis in mammals, the enzyme ribonucleotide reductase (RNR), impacts cancer susceptibility and serves as a target for anti-cancer therapies. Because RNR-regulated dNTP production can influence DNA replication fidelity while also supporting genome-protecting DNA repair, RNR has complex and stage-specific roles in carcinogenesis. Nevertheless, cancer cells are dependent on RNR for de novo dNTP biosynthesis. Therefore, elevated RNR expression is a characteristic of many cancers, and an array of mechanistically distinct RNR inhibitors serve as effective agents for cancer treatment. The dNTP metabolism machinery, including RNR, has been exploited for therapeutic benefit for decades and remains an important target for cancer drug development.
Collapse
Affiliation(s)
- Y Aye
- 1] Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA [2] Department of Biochemistry, Weill Cornell Medical College, New York, NY, USA
| | - M Li
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| | - M J C Long
- Graduate Program in Biochemistry, Brandeis University, Waltham, MA, USA
| | - R S Weiss
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| |
Collapse
|