 |
PDBsum entry 5ca2
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Lyase(oxo-acid)
|
PDB id
|
|
|
|
5ca2
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Conformational mobility of his-64 in the thr-200----Ser mutant of human carbonic anhydrase ii.
|
|
|
Authors
|
|
J.F.Krebs,
C.A.Fierke,
R.S.Alexander,
D.W.Christianson.
|
|
|
Ref.
|
|
Biochemistry, 1991,
30,
9153-9160.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The three-dimensional structure of the Thr-200----Ser (T200S) mutant of human
carbonic anhydrase II (CAII) has been determined by X-ray crystallographic
methods at 2.1-A resolution. This particular mutant of CAII exhibits CO2 hydrase
activity that is comparable to that of the wild-type enzyme with a 2-fold
stabilization of the E.HCO3- complex and esterase activity that is 4-fold
greater than that of the wild-type enzyme. The structure of the mutant enzyme
reveals no significant local changes accompanying the conservative T200S
substitution, but an important nonlocal structural change is evident: the side
chain of catalytic residue His-64 rotates away from the active site by 105
degrees about chi 1 and apparently displaces a water molecule. The displaced
water molecule is present in the wild-type enzyme; however, the electron density
into which this water is built is interpretable as an alternate conformation of
His-64 with 10-20% occupancy. The rate constants for proton transfer from the
zinc-water ligand to His-64 and from His-64 to bulk solvent are maintained in
the T200S variant; therefore, if His-64 is conformationally mobile about chi 1
and/or chi 2 during catalysis, compensatory changes in solvent configuration
must sustain efficient proton transfer.
|
|
|
|
|
|
|
