M. Nukaga et al., A SURVEY OF A FUNCTIONAL AMINO-ACID OF CLASS C-BETA-LACTAMASE CORRESPONDING TO GLU166 OF CLASS A-BETA-LACTAMASES, FEBS letters, 332(1-2), 1993, pp. 93-98
The class C beta-lactamase of Citrobacter freundii GN346 is a typical
cephalosporinase comprising 361 amino acids. The aspartic acid at posi
tion 217 and glutamic acid at position 219 in this beta-lactamase were
, respectively, previously shown not to be the counterpart of Glu166 (
ABL166) in class A beta-lactamases, even though sequence alignment of
class A and C enzymes strongly suggested this possibility [(1990) FEBS
Lett. 264,211-214; (1990) J. Bacteriol. 172, 4348-4351]. We tried aga
in to assign candidates for the counterpart of Glu166 through sequence
alignment based on other criteria, the glutamic acids at positions 19
5 and 205 in the class C beta-lactamase being selected. To investigate
this possibility, these two glutamic acids were changed to glutamine,
lysine or alanine, respectively. All the mutant enzymes showed more t
han 50% of the activity of the wild-type enzyme, indicating that the p
ossibility was ruled out. These results strongly suggested the possibi
lity that the class C beta-lactamase lacks a functional acidic residue
corresponding to Glu166 in class A enzymes.