5ca2
From Proteopedia
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| , resolution 2.1Å | |||||||
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| Ligands: | , | ||||||
| Activity: | Carbonate dehydratase, with EC number 4.2.1.1 | ||||||
| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||
CONFORMATIONAL MOBILITY OF HIS-64 IN THE THR-200 (RIGHT ARROW) SER MUTANT OF HUMAN CARBONIC ANHYDRASE II
Overview
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.
About this Structure
5CA2 is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.
Reference
Conformational mobility of His-64 in the Thr-200----Ser mutant of human carbonic anhydrase II., Krebs JF, Fierke CA, Alexander RS, Christianson DW, Biochemistry. 1991 Sep 24;30(38):9153-60. PMID:1909891
Page seeded by OCA on Mon Mar 31 05:40:55 2008
