pKa calculations for class C β-lactamases: The role of tyr-150

• Published in: Proteins, structure, function, and bioinformatics Vol. 40; no. 1; pp. 23 - 28
• Main Authors: Lamotte-Brasseur, Josette, Dubus, Alain, Wade, Rebecca C.
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01.07.2000
• Subjects: electrostatics; mechanism; Poisson-Boltzmann; protein modelling
• ISSN: 0887-3585; 1097-0134
• DOI: 10.1002/(SICI)1097-0134(20000701)40:1<23::AID-PROT40>3.0.CO;2-7

The Poisson‐Boltzmann method was used to compute the pKa values of titratable residues in a set of class C β‐lactamases. In these calculations, the pKa of the phenolic group of residue Tyr150 is the only one to stand out with an abnormally low value of 8.3, more than one pKa unit lower than the measured reference value for tyrosine in solution. Other important residues of the catalytic pocket, such as the conserved Lys67, Lys315, His314, and Glu272 (hydrogen‐bonded to the ammonium group of Lys315), display normal protonation states at neutral pH. pKa values were also computed in catalytically impaired β‐lactamase mutants. Comparisons between the relative kcat values and the Tyr150 pKa value in these mutants revealed a striking correlation. In active enzymes, this pKa value is always lower than the solution reference value while it is close to normal in inactive enzymes. These results thus support the hypothesis that the phenolate form of Tyr150 is responsible for the activation of the nucleophilic serine. The possible roles of Lys67 and Lys315 during catalysis are also discussed. Proteins 2000;40:23–28. © 2000 Wiley‐Liss, Inc.