1hqa
From Proteopedia
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ALKALINE PHOSPHATASE (H412Q)
Overview
Site-specific mutagenesis has been used to replace His-412 with glutamine, in Escherichia coli alkaline phosphatase. In the wild-type enzyme His-412, is a direct ligand to one of the catalytically important zinc atoms (Zn1), in the active site. The mutant enzyme (H412Q) exhibited about the same, k(cat), but a 50-fold increase in K(m) compared to the corresponding, kinetic parameters for the wild-type enzyme. Furthermore, the H412Q enzyme, had a lower zinc content than the wild-type enzyme. In contrast to the, wild-type enzyme, Tris was less effective in the transferase reaction and, dramatically inhibited the hydrolysis reaction of the H412Q enzyme. The, addition of zinc to the mutant enzyme increased the k(cat) value above, that of the wild-type enzyme, partially restored the weak substrate and, phosphate binding, and also alleviated the inhibition by Tris. The, structure of the H412Q enzyme was also determined by X-ray, crystallography. The overall structure of the H412Q enzyme was very, similar to that of the wild-type enzyme; the only alpha-carbon, displacements over 1 angstrom were observed near the mutation site. In the, H412Q structure no phosphate was bound in the active site of the enzyme;, however, two water molecules were observed where phosphate normally binds, in the wild-type enzyme. Close examination of the active site of the H412Q, structure revealed structural changes in Ser-102 as well as at the, mutation site. For example, the carbonyl oxygen of the side chain of, Gln-412 rotated away from the position of His-412 in the wild-type, structure, although too far away (3.2 angstroms) to coordinate to Zn1., Studies on the H412Q enzyme, and a comparison of the H412Q and H412N, structures, suggest that the structure and electostatics of the imidazole, ring of histidine are critical for its function as a zinc ligand in, alkaline phosphatase.
About this Structure
1HQA is a Single protein structure of sequence from Escherichia coli with ZN as ligand. Active as Alkaline phosphatase, with EC number 3.1.3.1 Full crystallographic information is available from OCA.
Reference
Kinetic and X-ray structural studies of a mutant Escherichia coli alkaline phosphatase (His-412-->Gln) at one of the zinc binding sites., Ma L, Kantrowitz ER, Biochemistry. 1996 Feb 20;35(7):2394-402. PMID:8652582
Page seeded by OCA on Tue Nov 20 16:44:28 2007
