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The Effect of DNA Topology on Observed Rates of R-Loop Formation and DNA Strand Cleavage by CRISPR Cas12a. Genes (Basel) 2019; 10:genes10020169. [PMID: 30813348 PMCID: PMC6409811 DOI: 10.3390/genes10020169] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 02/14/2019] [Accepted: 02/15/2019] [Indexed: 12/26/2022] Open
Abstract
Here we explored the mechanism of R-loop formation and DNA cleavage by type V CRISPR Cas12a (formerly known as Cpf1). We first used a single-molecule magnetic tweezers (MT) assay to show that R-loop formation by Lachnospiraceae bacterium ND2006 Cas12a is significantly enhanced by negative DNA supercoiling, as observed previously with Streptococcus thermophilus DGCC7710 CRISPR3 Cas9. Consistent with the MT data, the apparent rate of cleavage of supercoiled plasmid DNA was observed to be >50-fold faster than the apparent rates for linear DNA or nicked circular DNA because of topology-dependent differences in R-loop formation kinetics. Taking the differences into account, the cleavage data for all substrates can be fitted with the same apparent rate constants for the two strand-cleavage steps, with the first event >15-fold faster than the second. By independently following the ensemble cleavage of the non-target strand (NTS) and target strand (TS), we could show that the faster rate is due to NTS cleavage, the slower rate due to TS cleavage, as expected from previous studies.
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52
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Lubner JM, Balsbaugh JL, Church GM, Chou MF, Schwartz D. Characterizing Protein Kinase Substrate Specificity Using the Proteomic Peptide Library (ProPeL) Approach. ACTA ACUST UNITED AC 2019; 10:e38. [PMID: 29927115 DOI: 10.1002/cpch.38] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Characterizing protein kinase substrate specificity motifs represents a powerful step in elucidating kinase-signaling cascades. The protocol described here uses a bacterial system to evaluate kinase specificity motifs in vivo, without the need for radioactive ATP. The human kinase of interest is cloned into a heterologous bacterial expression vector and allowed to phosphorylate E. coli proteins in vivo, consistent with its endogenous substrate preferences. The cells are lysed, and the bacterial proteins are digested into peptides and phosphoenriched using bulk TiO2 . The pooled phosphopeptides are identified by tandem mass spectrometry, and bioinformatically analyzed using the pLogo visualization tool. The ProPeL approach allows for detailed characterization of wildtype kinase specificity motifs, identification of specificity drift due to kinase mutations, and evaluation of kinase residue structure-function relationships. © 2018 by John Wiley & Sons, Inc.
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Affiliation(s)
- Joshua M Lubner
- University of Connecticut, Department of Physiology and Neurobiology, Storrs, Connecticut
| | - Jeremy L Balsbaugh
- University of Connecticut, Proteomics & Metabolomics Facility, Center for Open Research Resources & Equipment, Storrs, Connecticut
| | - George M Church
- Harvard Medical School, Department of Genetics, Boston, Massachusetts and Wyss Institute for Biologically Inspired Engineering, Boston, Massachusetts
| | - Michael F Chou
- Harvard Medical School, Department of Genetics, Boston, Massachusetts and Wyss Institute for Biologically Inspired Engineering, Boston, Massachusetts
| | - Daniel Schwartz
- University of Connecticut, Department of Physiology and Neurobiology, Storrs, Connecticut
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53
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Winton AJ, Baptiste JL, Allen MA. A versatile expression vector for the growth and amplification of unmodified phage display polypeptides. Protein Expr Purif 2018; 149:31-36. [DOI: 10.1016/j.pep.2018.04.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 04/12/2018] [Accepted: 04/13/2018] [Indexed: 11/29/2022]
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54
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Oeemig JS, Ollila OS, Iwaï H. NMR structure of the C-terminal domain of TonB protein from Pseudomonas aeruginosa. PeerJ 2018; 6:e5412. [PMID: 30186676 PMCID: PMC6118199 DOI: 10.7717/peerj.5412] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Accepted: 07/19/2018] [Indexed: 11/20/2022] Open
Abstract
The TonB protein plays an essential role in the energy transduction system to drive active transport across the outer membrane (OM) using the proton-motive force of the cytoplasmic membrane of Gram-negative bacteria. The C-terminal domain (CTD) of TonB protein is known to interact with the conserved TonB box motif of TonB-dependent OM transporters, which likely induces structural changes in the OM transporters. Several distinct conformations of differently dissected CTDs of Escherichia coli TonB have been previously reported. Here we determined the solution NMR structure of a 96-residue fragment of Pseudomonas aeruginosa TonB (PaTonB-96). The structure shows a monomeric structure with the flexible C-terminal region (residues 338-342), different from the NMR structure of E. coli TonB (EcTonB-137). The extended and flexible C-terminal residues are confirmed by 15N relaxation analysis and molecular dynamics simulation. We created models for the PaTonB-96/TonB box interaction and propose that the internal fluctuations of PaTonB-96 makes it more accessible for the interactions with the TonB box and possibly plays a role in disrupting the plug domain of the TonB-dependent OM transporters.
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Affiliation(s)
- Jesper S. Oeemig
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
- VIB Center for Structural Biology, Vlaams Instituut voor Biotechnologie (VIB), Vrije Universiteit Brussel, Brussels, Belgium
| | - O.H. Samuli Ollila
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Hideo Iwaï
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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55
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Norppa AJ, Kauppala TM, Heikkinen HA, Verma B, Iwaï H, Frilander MJ. Mutations in the U11/U12-65K protein associated with isolated growth hormone deficiency lead to structural destabilization and impaired binding of U12 snRNA. RNA (NEW YORK, N.Y.) 2018; 24:396-409. [PMID: 29255062 PMCID: PMC5824358 DOI: 10.1261/rna.062844.117] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 12/12/2017] [Indexed: 05/09/2023]
Abstract
Mutations in the components of the minor spliceosome underlie several human diseases. A subset of patients with isolated growth hormone deficiency (IGHD) harbors mutations in the RNPC3 gene, which encodes the minor spliceosome-specific U11/U12-65K protein. Although a previous study showed that IGHD patient cells have defects in U12-type intron recognition, the biochemical effects of these mutations on the 65K protein have not been characterized. Here, we show that a proline-to-threonine missense mutation (P474T) and a nonsense mutation (R502X) in the C-terminal RNA recognition motif (C-RRM) of the 65K protein impair the binding of 65K to U12 and U6atac snRNAs. We further show that the nonsense allele is targeted to the nonsense-mediated decay (NMD) pathway, but in an isoform-specific manner, with the nuclear-retained 65K long-3'UTR isoform escaping the NMD pathway. In contrast, the missense P474T mutation leads, in addition to the RNA-binding defect, to a partial defect in the folding of the C-RRM and reduced stability of the full-length protein, thus reducing the formation of U11/U12 di-snRNP complexes. We propose that both the C-RRM folding defect and NMD-mediated decrease in the levels of the U11/U12-65K protein reduce formation of the U12-type intron recognition complex and missplicing of a subset of minor introns leading to pituitary hypoplasia and a subsequent defect in growth hormone secretion.
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Affiliation(s)
- Antto J Norppa
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Tuuli M Kauppala
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Harri A Heikkinen
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Bhupendra Verma
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Hideo Iwaï
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
| | - Mikko J Frilander
- Institute of Biotechnology, FI-00014 University of Helsinki, Finland
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56
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Fujita-Yamaguchi Y, Bagramyan K, Yamaguchi Y, Ikeda A, Dohmae N, Hong TB, Kalkum M. Mass spectrometric revival of an l-rhamnose- and d-galactose-specific lectin from a lost strain of Streptomyces. J Biol Chem 2018; 293:368-378. [PMID: 29101228 DOI: 10.1074/jbc.m117.812719] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 11/02/2017] [Indexed: 11/06/2022] Open
Abstract
Blood type B-specific Streptomyces sp. 27S5 hemagglutinin (SHA) was discovered and characterized in the 1970s. Although strain 27S5 has been lost, the purified SHA protein survived intact under frozen conditions and retained its activity. Using modern techniques, here we further characterized SHA. Fourier-transform ion cyclotron resonance MS analysis determined the average molecular mass of SHA as 13,314.67 Da. MS of digested SHA peptides, Streptomyces genomic database matching, and N-terminal sequencing solved the 131-residue amino acid sequence of SHA. We found that SHA is homologous to N-terminally truncated hypothetical proteins encoded by the genomes of Streptomyces lavendulae, Streptomyces sp. Mg1, and others. The gene of the closest homologue in S. lavendulae, a putative polysaccharide deacetylase (PDSL), encodes 68 additional N-terminal amino acids, and its C terminus perfectly matched the SHA sequence, except for a single Ala-to-Glu amino acid difference. We expressed recombinant SHA(PDSL-A108E) (rSHA) as an enzymatically cleavable fusion protein in Escherichia coli, and glycan microarray analyses indicated that refolded rSHA exhibits the blood type B- and l-rhamnose-specific characteristics of authentic SHA, confirming that rSHA is essentially identical with SHA produced by Streptomyces sp. 27S5. We noted that SHA comprises three similar domains, representing 70% of the protein, and that these SHA domains partially overlap with annotated clostridial hydrophobic with conserved W domains. Furthermore, examination of GFP-tagged SHA revealed binding to microbial surfaces. rSHA may be useful both for studying the role of SHA/clostridial hydrophobic with conserved W domains in carbohydrate binding and for developing novel diagnostics and therapeutics for l-rhamnose-containing microorganisms.
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Affiliation(s)
- Yoko Fujita-Yamaguchi
- Department of Molecular & Cellular Biology, Duarte, California 91010; Department of Diabetes Complications & Metabolism, Duarte, California 91010.
| | - Karine Bagramyan
- Department of Molecular Immunology, Beckman Research Institute of City of Hope, Duarte, California 91010
| | - Yoshiki Yamaguchi
- Structural Glycobiology Team, Systems Glycobiology Research Group, RIKEN Global Research Cluster, RIKEN, Saitama 351-0198, Japan
| | - Akemi Ikeda
- Structural Glycobiology Team, Systems Glycobiology Research Group, RIKEN Global Research Cluster, RIKEN, Saitama 351-0198, Japan
| | - Naoshi Dohmae
- Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science, RIKEN, Saitama 351-0198, Japan
| | - Teresa B Hong
- Department of Molecular Immunology, Beckman Research Institute of City of Hope, Duarte, California 91010
| | - Markus Kalkum
- Department of Molecular Immunology, Beckman Research Institute of City of Hope, Duarte, California 91010.
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57
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Iwaï H, Mikula KM, Oeemig JS, Zhou D, Li M, Wlodawer A. Structural Basis for the Persistence of Homing Endonucleases in Transcription Factor IIB Inteins. J Mol Biol 2017; 429:3942-3956. [PMID: 29055778 PMCID: PMC6309676 DOI: 10.1016/j.jmb.2017.10.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 09/29/2017] [Accepted: 10/12/2017] [Indexed: 11/19/2022]
Abstract
Inteins are mobile genetic elements that are spliced out of proteins after translation. Some inteins contain a homing endonuclease (HEN) responsible for their propagation. Hedgehog/INTein (HINT) domains catalyzing protein splicing and their nested HEN domains are thought to be functionally independent because of the existence of functional mini-inteins without HEN domains. Despite the lack of obvious mutualism between HEN and HINT domains, HEN domains are persistently found at one specific site in inteins, indicating their potential functional role in protein splicing. Here we report crystal structures of inactive and active mini-inteins derived from inteins residing in the transcription factor IIB of Methanococcus jannaschii and Methanocaldococcus vulcanius, revealing a novel modified HINT fold that might provide new insights into the mutualism between the HEN and HINT domains. We propose an evolutionary model of inteins and a functional role of HEN domains in inteins.
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Affiliation(s)
- Hideo Iwaï
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki FIN-00014, Finland.
| | - Kornelia M Mikula
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki FIN-00014, Finland
| | - Jesper S Oeemig
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki FIN-00014, Finland
| | - Dongwen Zhou
- Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD 21702, USA
| | - Mi Li
- Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD 21702, USA; Basic Science Program, Leidos Biomedical Research, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Alexander Wlodawer
- Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD 21702, USA.
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58
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de Araujo ED, Manaswiyoungkul P, Israelian J, Park J, Yuen K, Farhangi S, Berger-Becvar A, Abu-Jazar L, Gunning PT. High-throughput thermofluor-based assays for inhibitor screening of STAT SH2 domains. J Pharm Biomed Anal 2017; 143:159-167. [DOI: 10.1016/j.jpba.2017.04.052] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 04/27/2017] [Accepted: 04/30/2017] [Indexed: 11/24/2022]
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59
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Mikula KM, Tascón I, Tommila JJ, Iwaï H. Segmental isotopic labeling of a single-domain globular protein without any refolding step by an asparaginyl endopeptidase. FEBS Lett 2017; 591:1285-1294. [PMID: 28369872 DOI: 10.1002/1873-3468.12640] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 03/23/2017] [Accepted: 03/24/2017] [Indexed: 01/23/2023]
Abstract
Asparaginyl endopeptidases (AEPs) catalyze head-to-tail backbone cyclization of naturally occurring cyclic peptides such as cyclotides, and have become an important peptide-engineering tool for macrocyclization and peptide ligation. Here, we report efficient protein ligation in trans by mimicking efficient backbone cyclization by an AEP without any excess of reactants. We demonstrate a practical application of segmental isotopic labeling for NMR studies of a single-domain globular protein without any refolding step using the recombinant AEP prepared from Escherichia coli. This simple protein ligation approach using an AEP could be applied for incorporation of various biophysical probes into proteins as well as post-translational production of full-length proteins.
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Affiliation(s)
- Kornelia M Mikula
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Finland
| | - Igor Tascón
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Finland
| | - Jenni J Tommila
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Finland
| | - Hideo Iwaï
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Finland
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60
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Strategies for over-expression and purification of recombinant full length STAT5B in Escherichia coli. Protein Expr Purif 2017; 129:1-8. [DOI: 10.1016/j.pep.2016.08.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Revised: 08/24/2016] [Accepted: 08/29/2016] [Indexed: 11/21/2022]
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61
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Yadav DK, Yadav N, Yadav S, Haque S, Tuteja N. An insight into fusion technology aiding efficient recombinant protein production for functional proteomics. Arch Biochem Biophys 2016; 612:57-77. [DOI: 10.1016/j.abb.2016.10.012] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 10/15/2016] [Accepted: 10/18/2016] [Indexed: 11/27/2022]
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62
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Ciragan A, Aranko AS, Tascon I, Iwaï H. Salt-inducible Protein Splicing in cis and trans by Inteins from Extremely Halophilic Archaea as a Novel Protein-Engineering Tool. J Mol Biol 2016; 428:4573-4588. [PMID: 27720988 DOI: 10.1016/j.jmb.2016.10.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Revised: 09/29/2016] [Accepted: 10/01/2016] [Indexed: 10/20/2022]
Abstract
Intervening protein sequences (inteins) from extremely halophilic haloarchaea can be inactive under low salinity but could be activated by increasing the salt content to a specific concentration for each intein. The halo-obligatory inteins confer high solubility under both low and high salinity conditions. We showed the broad utility of salt-dependent protein splicing in cis and trans by demonstrating backbone cyclization, self-cleavage for purification, and scarless protein ligation for segmental isotopic labeling. Artificially split MCM2 intein derived from Halorhabdus utahensis remained highly soluble and was capable of protein trans-splicing with excellent ligation kinetics by reassembly under high salinity conditions. Importantly, the MCM2 intein has the active site residue of Ser at the +1 position, which remains in the ligated product, instead of Cys as found in many other efficient split inteins. Since Ser is more abundant than Cys in proteins, the novel split intein could widen the applications of segmental labeling in protein NMR spectroscopy and traceless protein ligation by exploiting a Ser residue in the native sequences as the +1 position of the MCM2 intein. The split halo-obligatory intein was successfully used to demonstrate the utility in NMR investigation of intact proteins by producing segmentally isotope-labeled intact TonB protein from Helicobacter pylori.
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Affiliation(s)
- Annika Ciragan
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki, FI-00014, Finland
| | - A Sesilja Aranko
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki, FI-00014, Finland
| | - Igor Tascon
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki, FI-00014, Finland
| | - Hideo Iwaï
- Research Program in Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P.O. Box 65, Helsinki, FI-00014, Finland.
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63
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Baranova N, Loose M. Single-molecule measurements to study polymerization dynamics of FtsZ-FtsA copolymers. Methods Cell Biol 2016; 137:355-370. [PMID: 28065316 DOI: 10.1016/bs.mcb.2016.03.036] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Bacterial cytokinesis is commonly initiated by the Z-ring, a dynamic cytoskeletal structure that assembles at the site of division. Its primary component is FtsZ, a tubulin-like GTPase, that like its eukaryotic relative forms protein filaments in the presence of GTP. Since the discovery of the Z-ring 25years ago, various models for the role of FtsZ have been suggested. However, important information about the architecture and dynamics of FtsZ filaments during cytokinesis is still missing. One reason for this lack of knowledge has been the small size of bacteria, which has made it difficult to resolve the orientation and dynamics of individual FtsZ filaments in the Z-ring. While superresolution microscopy experiments have helped to gain more information about the organization of the Z-ring in the dividing cell, they were not yet able to elucidate a mechanism of how FtsZ filaments reorganize during assembly and disassembly of the Z-ring. In this chapter, we explain how to use an in vitro reconstitution approach to investigate the self-organization of FtsZ filaments recruited to a biomimetic lipid bilayer by its membrane anchor FtsA. We show how to perform single-molecule experiments to study the behavior of individual FtsZ monomers during the constant reorganization of the FtsZ-FtsA filament network. We describe how to analyze the dynamics of single molecules and explain why this information can help to shed light onto possible mechanism of Z-ring constriction. We believe that similar experimental approaches will be useful to study the mechanism of membrane-based polymerization of other cytoskeletal systems, not only from prokaryotic but also eukaryotic origin.
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Affiliation(s)
- N Baranova
- Institute for Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - M Loose
- Institute for Science and Technology Austria (IST Austria), Klosterneuburg, Austria
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64
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Abstract
Lysine acetylation serves as an epigenetic marker for myriad cellular processes, such as signaling, differentiation, DNA repair, angiogenesis, and the like. Sirtuin 1 (SIRT1) and sirtuin 2 (SIRT2) are NAD(+)-dependent histone deacetylases that operate as post-translational regulators for the deacetylation of acetyllysine. Here, we discuss the ability for SIRT1 and SIRT2 to deacetylate monoacetylated histone H3 on two separate architectures-the peptide and the nucleosome. In addition, we analyze the site-specificity of SIRT1 and SIRT2 on 10 different monoacetylated histone H3 nucleosomes. By utilizing a rapid screening array, SIRT1 and SIRT2 were found to demonstrate heightened enzymatic activity when incubated with nucleosomal substrates over their peptide counterparts. These two enzymes displayed little site-specificity among the acetyl-nucleosomes screened, contrary to previous expectations, as well. The implication of the overall nonspecificity of SIRT1 and SIRT2 on the nucleosome suggests that these sirtuin enzymes have an adaptive nature, harnessing an ability to respond to various cellular situations, rather than an enzyme specifically designed for a particular task or function.
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Affiliation(s)
- Willie W. Hsu
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - Bo Wu
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - Wenshe R. Liu
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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