On the basis of chemical modification and X-ray
crystallography, glutamic acid at position 58
(Glu-58) of ribonuclease T
1 (RNase T
1) has been
identified as a catalytic residue. On the other hand,
the mutant of RNase T
1 in which Glu-58 is replaced
with aspartic acid (Glu58Asp RNase T
1) or alanine
(Glu58Ala RNase T
1) did not lose the enzymatic
activity 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 complexes of guanosine 3'-monophosphate
(3'-GMP) with Glu58Asp and Glu58Ala RNase T
1.
The conformation thus obtained was compared
with that of the complex of 3'-GMP and wild-type
RNase T
1. The results indicated that upon replacement
of Glu-58 with Asp or Ala, the relative position
of His-40 to 3'-GMP in the active site change in
such a way that His-40 acts as a general base
catalyst.
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