Subunit interface of triosephosphate isomerase: site-directed mutagenesis and characterization of the altered enzyme.
We have replaced asparagine residues at the subunit interface of yeast triosephosphate isomerase ( TIM) using site-directed mutagenesis in order to elucidate the effects of substitutions on the catalytic activity and conformational stability of the enzyme. The mutant proteins were expressed in a strain of Escherichia coli lacking the bacterial isomerase and purified by ion-exchange and immunoadsorption chromatography. Single replacements of Asn-78 by either Thr or Ile residues had little effect on the enzyme's catalytic efficiency, while the single replacement Asn-78----Asp-78 and the double replacement Asn-14/Asn-78----Thr-14/Ile-78 appreciably lowered kcat for the substrate D-glyceraldehyde 3-phosphate. The isoelectric point of the mutant Asn-78----Asp-78 was equivalent to that of wild-type yeast TIM that had undergone a single, heat-induced deamidation, and this mutant enzyme was less resistant than wild-type TIM to denaturation and inactivation caused by elevated temperature, denaturants, tetrabutylammonium bromide, alkaline pH, and proteases.[1]References
- Subunit interface of triosephosphate isomerase: site-directed mutagenesis and characterization of the altered enzyme. Casal, J.I., Ahern, T.J., Davenport, R.C., Petsko, G.A., Klibanov, A.M. Biochemistry (1987) [Pubmed]
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