Primary Citation of Related Structures: 1UIP, 1UIO
PubMed Abstract:
His 238, a conserved amino acid located in hydrogen-bonding distance from C-6 of the substrate in the active site of murine adenosine deaminase (mADA) and postulated to play an important role in catalysis, was altered into an alanine, a glutamate, and an arginine using site-directed mutagenesis ...
His 238, a conserved amino acid located in hydrogen-bonding distance from C-6 of the substrate in the active site of murine adenosine deaminase (mADA) and postulated to play an important role in catalysis, was altered into an alanine, a glutamate, and an arginine using site-directed mutagenesis. The Ala and Glu substitutions did not result in changes of the secondary or tertiary structure, while the Arg mutation caused local perturbations in tertiary structure and quenched the emission of one or more enzyme tryptophans. Neither the Glu or Arg mutations affected substrate binding affinity. By contrast, the Ala mutation enhanced substrate and inhibitor binding by 20-fold. The most inactive of the mutants, Glu 238, had a kcat/K(m) 4 x 10(-6) lower than the wild-type value, suggesting that a positive charge on His 238 is important for proper catalytic function. The Ala 238 mutant was the most active ADA, with a kcat/K(m) 2 x 10(-3) lower than the wild-type value. NMR spectroscopy and crystallography revealed that this mutant is able to catalyze hydration of purine riboside, a ground-state analog of the reaction. These results collectively show that His 238 is not required for formation of the hydroxylate used in the deamination and may instead have an important electrostatic role.
Related Citations:
Probing the Functional Role of Two Conserved Active Site Aspartates in Mouse Adenosine Deaminase Sideraki, V., Mohamedali, K.A., Wilson, D.K., Chang, Z., Kellems, R.E., Quiocho, F.A., Rudolph, F.B. (1996) Biochemistry 35: 7862
A Pre-Transition-State Mimic of an Enzyme: X-Ray Structure of Adenosine Deaminase with Bound 1-Deazaadenosine and Zinc-Activated Water Wilson, D.K., Quiocho, F.A. (1993) Biochemistry 32: 1689
Atomic Structure of Adenosine Deaminase Complexed with a Transition-State Analog: Understanding Catalysis and Immunodeficiency Mutations Wilson, D.K., Rudolph, F.B., Quiocho, F.A. (1991) Science 252: 1278
Organizational Affiliation:
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA.
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