Abstract
By carboxymethylation at the γ-carboxyl group of
glutamic acid-58, ribonuclease T1 (RNase T1) loses
its enzymatic activity entirely while retaining
substrate-binding ability almost completely. To elucidate
the mechanism of this phenomenon as based
on the three-dimensional structure, molecular dynamics
simulation and energy minimization calculation
were carried out for the complex of
guanosine 2'-monophosphate (2'-GMP) with carboxymethylated
RNase T1. The conformation thus
obtained was compared with that of the complex of
2'-GMP and intact RNase T1. The results indicated
that upon carboxymethylation the guanine-binding
loop (histidine-40 to phenylalanine-48) is displaced
to open the active site cleft so that 2'-GMP binds to
the active site in such a way that the phosphate
group of the inhibitor moves away from the active
site residues, glutamic acid-58 and arginine-77.
