title: Adenosine deaminase prefers a distinct sugar ring conformation for binding and catalysis: kinetic and structural studies.
abstract: Several recent X-ray crystal structures of adenosine deaminase (ADA) in complex with various adenosine surrogates have illustrated the preferred mode of substrate binding for this enzyme. To define more specific structural details of substrate preferences for binding and catalysis, we have studied the ADA binding efficiencies and deamination kinetics of several synthetic adenosine analogues in which the furanosyl ring is biased toward a particular conformation. NMR solution studies and pseudorotational analyses were used to ascertain the preferred furanose ring puckers (P, nu(MAX)) and rotamer distributions (chi and gamma) of the nucleoside analogues. It was shown that derivatives which are biased toward a "Northern" (3'-endo, N) sugar ring pucker were deaminated up to 65-fold faster and bound more tightly to the enzyme than those that preferred a "Southern" (2'-endo, S) conformation. This behavior, however, could be modulated by other structural factors. Similarly, purine riboside inhibitors of ADA that prefer the N hemisphere were more potent inhibitors than S analogues. These binding propensities were corroborated by detailed molecular modeling studies. Docking of both N- and S-type analogues into the ADA crystal structure coordinates showed that N-type substrates formed a stable complex with ADA, whereas for S-type substrates, it was necessary for the sugar pucker to adjust to a 3'-endo (N-type) conformation to remain in the ADA substrate binding site. These data outline the intricate structural details for optimum binding in the catalytic cleft of ADA.
authors.affiliation: Laboratory of Medicinal Chemistry, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
authors.forename: H
authors.initials: H
authors.lastname: Ford
authors.forename: F
authors.initials: F
authors.lastname: Dai
authors.forename: L
authors.initials: L
authors.lastname: Mu
authors.forename: M A
authors.initials: MA
authors.lastname: Siddiqui
authors.forename: M C
authors.initials: MC
authors.lastname: Nicklaus
authors.forename: L
authors.initials: L
authors.lastname: Anderson
authors.forename: V E
authors.initials: VE
authors.lastname: Marquez
authors.forename: J J
authors.initials: JJ
authors.lastname: Barchi
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000737:chemistry* / Q000378:metabolism*; D058892:Adenosine Deaminase Inhibitors; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002417:Cattle; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D011522:Protons; D013379:Substrate Specificity
chemical_list: D058892:Adenosine Deaminase Inhibitors; D004791:Enzyme Inhibitors; D011522:Protons; D000243:Adenosine Deaminase; D000241:Adenosine