1yjs
From Proteopedia
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K226Q Mutant Of Serine Hydroxymethyltransferase From B. Stearothermophilus, Complex With Glycine
Overview
Serine hydroxymethyltransferase (SHMT), a pyridoxal 5'-phosphate, (PLP)-dependent enzyme catalyzes the reversible conversion of l-Ser and, tetrahydropteroylglutamate (H(4)PteGlu) to Gly and 5,10-methylene, tetrahydropteroylglutamate (CH(2)-H(4)PteGlu). Biochemical and structural, studies on this enzyme have implicated several residues in the catalytic, mechanism, one of them being the active site lysine, which anchors PLP. It, has been proposed that this residue is crucial for product expulsion., However, in other PLP-dependent enzymes, the corresponding residue has, been implicated in the proton abstraction step of catalysis. In the, present investigation, Lys-226 of Bacillus stearothermophilus SHMT, (bsSHMT) was mutated to Met and Gln to evaluate the role of this residue, in catalysis. The mutant enzymes contained 1 mol of PLP per mol of subunit, suggesting that Schiff base formation with lysine is not essential for PLP, binding. The 3D structure of the mutant enzymes revealed that PLP was, bound at the active site in an orientation different from that of the, wild-type enzyme. In the presence of substrate, the PLP ring was in an, orientation superimposable with that of the external aldimine complex of, wild-type enzyme. However, the mutant enzymes were inactive, and the, kinetic analysis of the different steps of catalysis revealed that there, was a drastic reduction in the rate of formation of the quinonoid, intermediate. Analysis of these results along with the crystal structures, suggested that K-226 is responsible for flipping of PLP from one, orientation to another which is crucial for H(4)PteGlu-dependent, Calpha-Cbeta bond cleavage of l-Ser.
About this Structure
1YJS is a Protein complex structure of sequences from Geobacillus stearothermophilus with PLP as ligand. Active as Glycine hydroxymethyltransferase, with EC number 2.1.2.1 Full crystallographic information is available from OCA.
Reference
Role of Lys-226 in the catalytic mechanism of Bacillus stearothermophilus serine hydroxymethyltransferase--crystal structure and kinetic studies., Bhavani S, Trivedi V, Jala VR, Subramanya HS, Kaul P, Prakash V, Appaji Rao N, Savithri HS, Biochemistry. 2005 May 10;44(18):6929-37. PMID:15865438
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