Refined 2.5 Å structure of murine adenosine deaminase at pH 6.0

• Published in: Journal of molecular biology Vol. 226; no. 4; pp. 917 - 921
• Main Authors: SHARFF, A. J, WILSON, D. K, CHANG, Z, QUIOCHO, F. A
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier 20.08.1992
• Subjects: Adenosine Deaminase - chemistry; Adenosine Deaminase - metabolism; Animals; Binding Sites; Biological and medical sciences; Crystalline structure; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Ligands; Mice; Models, Molecular; Molecular biophysics; Protein Conformation; Purine Nucleosides - chemistry; Purine Nucleosides - metabolism; Ribonucleosides - chemistry; Ribonucleosides - metabolism; Structure in molecular biology; X-Ray Diffraction; Enzyme; Rodentia; Refinement; Environmental factor; Adenosine deaminase; X ray diffraction; Vertebrata; Mammalia; Mouse; Analog; Transition state; pH; Molecular complex; Crystalline structure
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(92)91040-V

The X-ray structure of murine adenosine deaminase complexed with the transition-state analogue 6-hydroxyl-1,6-dihydropurine ribonucleoside has been determined from a single crystal grown at pH 4.2 and transferred to mother liquor of increasing pH up to a final pH of 6.0 prior to data collection. The structure has been refined to 2.5 A to a final crystallographic R-factor of 20% using phases from the previously refined 2.4 A structure at pH 4.2. Kinetic measurements show that the enzyme is only 20% active at pH 4.2 whereas it is fully active between pH 6.0 and pH 8.5. The refined structures at either pH are essentially the same. Consideration of the pKa values of the key catalytic residues and the mechanism proposed on the basis of the structure suggests that the ionization state of these residues is largely responsible for the pH dependence on activity.