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Title: Active Site and Remote Contributions to Catalysis in Methylthioadenosine Nucleosidases

5'-Methylthioadenosine/S-adenosyl-l-homocysteine nucleosidases (MTANs) catalyze the hydrolysis of 5'-methylthioadenosine to adenine and 5-methylthioribose. The amino acid sequences of the MTANs from Vibrio cholerae (VcMTAN) and Escherichia coli (EcMTAN) are 60% identical and 75% similar. Protein structure folds and kinetic properties are similar. However, binding of transition-state analogues is dominated by favorable entropy in VcMTAN and by enthalpy in EcMTAN. Catalytic sites of VcMTAN and EcMTAN in contact with reactants differ by two residues; Ala113 and Val153 in VcMTAN are Pro113 and Ile152, respectively, in EcMTAN. Here, we mutated the VcMTAN catalytic site residues to match those of EcMTAN in anticipation of altering its properties toward EcMTAN. Inhibition of VcMTAN by transition-state analogues required filling both active sites of the homodimer. However, in the Val153Ile mutant or double mutants, transition-state analogue binding at one site caused complete inhibition. Therefore, a single amino acid, Val153, alters the catalytic site cooperativity in VcMTAN. The transition-state analogue affinity and thermodynamics in mutant VcMTAN became even more unlike those of EcMTAN, the opposite of expectations from catalytic site similarity; thus, catalytic site contacts in VcMTAN are unable to recapitulate the properties of EcMTAN. X-ray crystal structures of EcMTAN, VcMTAN, and a multiple-site mutant of VcMTAN mostmore » closely resembling EcMTAN in catalytic site contacts show no major protein conformational differences. In conclusion, the overall protein architectures of these closely related proteins are implicated in contributing to the catalytic site differences.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [1]
  1. Albert Einstein College of Medicine, Bronx, NY (United States). Dept. of Biochemistry
  2. Victoria Univ. of Wellington (New Zealand). Ferrier Research Inst.
Publication Date:
OSTI Identifier:
1186919
Grant/Contract Number:
AC02-06CH11357; GM41916; GM068036; P41RR012408; P41GM103473
Type:
Accepted Manuscript
Journal Name:
Biochemistry
Additional Journal Information:
Journal Volume: 54; Journal Issue: 15; Journal ID: ISSN 0006-2960
Publisher:
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH)
Country of Publication:
United States
Language:
ENGLISH
Subject:
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY