Role of pro-297 in the catalytic mechanism of sheep liver serine hydroxymethyltransferase

Talwar, Rashmi and Leelavathy, Vijayapandian and Rao, Jala VK and Rao, Naropantul Appaji and Savithri, Handanahal S (2000) Role of pro-297 in the catalytic mechanism of sheep liver serine hydroxymethyltransferase. In: Biochemical Journal, 350 . pp. 849-853.

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Abstract

Serine hydroxymethyltransferase belongs to the a class of pyridoxal-5´-phosphate enzymes along with aspartate aminotransferase. Recent reports on the three-dimensional structure of human liver cytosolic serine hydroxymethyltransferase had suggested a high degree of similarity between the active-site geometries of the two enzymes. A comparison of the sequences of serine hydroxymethyltransferases revealed the presence of several highly conserved residues, including Pro-297. This residue is equivalent to residue Arg-292 of aspartate aminotransferase, which binds the c-carboxy group of aspartate. In an attempt to change the reaction speciÆcity of the hydroxymethyltransferase to that of an aminotransferase and to assign a possible reason for the conserved nature of Pro-297, it was mutated to Arg. The mutation decreased the hydroxymethyltransferase activity signiÆ-cantly (by 85±90%) and abolished the ability to catalyse alternative reactions, without alteration in the oligomeric structure, pyridoxal 5´-phosphate content or substrate binding. However, the concentration of the quinonoid intermediate and the extent of proton exchange was decreased considerably (by approx.85%) corresponding to the decrease in catalytic activity. Interestingly,mutant Pro-297 Arg was unable to perform the transamination reaction with l-aspartate. All these results suggest that although Pro-297 is indirectly involved in catalysis, it might not have any role in imparting substrate speciÆcity, unlike the similarly positioned Arg-292 in aspartate aminotransferase.

Item Type:	Journal Article
Publication:	Biochemical Journal
Publisher:	Portland Press
Additional Information:	Mounted on the Internet with permission from Portland Press (2000).
Keywords:	proton abstraction;pyridoxal-5´-phosphate;reaction specificity;site-directed mutagenesis
Department/Centre:	Division of Biological Sciences > Biochemistry
Date Deposited:	06 Sep 2004
Last Modified:	19 Sep 2010 04:15
URI:	http://eprints.iisc.ac.in/id/eprint/1769

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