The sulfurtransferase activity and structure of rhodanese are affected by site-directed replacement of Arg-186 or Lys-249

Luo, G.X.; Horowitz, P.M.

Journal of Biological Chemistry 269(11): 8220-8225


ISSN/ISBN: 0021-9258
PMID: 8132546
Accession: 009629742

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Two mutants of the enzyme rhodanese that replace Arg-186 with Leu (R186L) or Lys-249 with Ala (K249A) were prepared to test suggestions that these residues are involved in catalysis and structure. The predominant effect with R186L was functional, and K-m for the sulfur donor, thiosulfate, increased from 3.7 mm to 73 mm with a modest decrease in V-max (672 IU/mg to 576 IU/mg). However, K249A was virtually inactive using thiosulfate, but it was active with thiosulfonates such as p-toluene-, 2-aminoethane-, or ethanethiosulfonate, and these compounds could be demonstrated to form persulfide-substituted rhodanese. Compared with wild type enzyme, K249A had (a) reduced stability, (b) comparable secondary structure, (c) more easily exposed hydrophobic surfaces, and (d) a core structure that denatured similarly to the wild type enzyme. Thus, Arg-186 and Lys-249 are important in rhodanese catalysis, and Lys-249 is particularly critical for substrate selectivity and protein stability. Finally, the results suggest that there can be active rhodanese species in vivo that will be undetected using thiosulfate as a sulfur donor.