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pK a calculations for class C β‐lactamases: The role of tyr‐150
Author(s) -
LamotteBrasseur Josette,
Dubus Alain,
Wade Rebecca C.
Publication year - 2000
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/(sici)1097-0134(20000701)40:1<23::aid-prot40>3.0.co;2-7
Subject(s) - chemistry , residue (chemistry) , stereochemistry , protonation , serine , enzyme , nucleophile , catalysis , tyrosine , biochemistry , organic chemistry , ion
The Poisson‐Boltzmann method was used to compute the pK a values of titratable residues in a set of class C β‐lactamases. In these calculations, the pK a 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 pK a 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. pK a values were also computed in catalytically impaired β‐lactamase mutants. Comparisons between the relative k cat values and the Tyr150 pK a value in these mutants revealed a striking correlation. In active enzymes, this pK a 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.