Polymorphic variants of human rhodanese exhibit differences in thermal stability and sulfurtransfer kinetics [Enzymology]

August 12th, 2015 by Libiad, M., Sriraman, A., Banerjee, R.

Rhodanese is a component of the mitochondrial hydrogen sulfide (H2S) oxidation pathway. Rhodanese catalyzes the transfer of sulfane sulfur from glutathione persulfide (GSSH) to sulfite generating thiosulfate and from thiosulfate to cyanide generating thiocyanate. Two polymorphic variations have been identified in the rhodanese coding sequence in the French Caucasian population. The first, 306A→C, has an allelic frequency of 1 percent and results in an E102D substitution in the encoded protein. The second polymorphism 853C→G, has an allelic frequency of 5 percent and leads to a P285A substitution. In this study, we have examined differences in the stability between wild-type rhodanese and the E102D and P285A variants and in the kinetics of the sulfurtransfer reactions. The Asp102 and Ala285 variants are more stable than wild-type rhodanese and exhibit kcat/KM,CN values that are 17 and 1.6 fold higher, respectively. All three rhodanese forms preferentially catalyze sulfurtransfer from GSSH to sulfite, generating thiosulfate and glutathione. The kcat/KM,sulfite values for the variants in the sulfurtransfer reaction from GSSH to sulfite were 1.6 (Asp102) and 4 fold (Ala285) lower than for wild-type rhodanese while the kcat/KM,GSSH values were similar for all three enzymes. Thiosulfate-dependent H2S production in murine liver lysate is low, consistent with a role for rhodanese in sulfide oxidation. Our studies show that polymorphic variations that are distant from the active site differentially modulate the sulfurtransferase activity of human rhodanese to cyanide versus sulfite and might be important in differences in susceptibility to diseases where rhodanese dysfunction has been implicated, e.g. inflammatory bowel diseases.