Kinetics of cyanide binding as a probe of local stability/flexibility of cytochrome

Rastislav Varhač , Nataša Tomášková , Marián Fabián , Erik Sedlák

Effect of anions of Hofmeister series (thiocyanate, perchlorate, iodide, bromide, nitrate, chloride, sulfate, and phosphate) on local and global stability and flexibility of horse heart ferricytochrome (cyt ) has been studied. Global stability of cyt was determined by iso/thermal denaturations monitored by change in ellipticity in the far-UV region and its local stability was determined from absorbance changes in the Soret region. Particularly, relative stability/flexibility of the Met80-heme iron bond has been assessed by analysis of binding of cyanide into the heme iron. Both global and local stabilities of cyt exhibited monotonous increase induced by a change of anion from chaotropic to kosmotropic species. However, this monotonous dependence was not observed for the rate constants of cyanide association with cyt . As expected more chaotropic ions induced lower stability of protein and faster binding of cyanide but this correlation was reversed for kosmotropic anions. We propose that the unusual bell-shaped dependence of rate constant of cyanide association is a result of modulation of Met80-heme iron bond strength and/or flexibility of heme region by Hofmeister anions independently on global stability of cyt . Further, our results demonstrate sensitivity of cyanide binding to local change in stability/flexibility in heme region of cyt .

Mots clés: cyt; MCD; flexibility; protein dynamics; ligand binding; Hofmeister series

Rastislav Varhač, Nataša Tomášková, Marián Fabián, Erik Sedlák. Kinetics of cyanide binding as a probe of local stability/flexibility of cytochrome. Biophysical Chemistry, 2009, 144 (1-2), pp.21. ⟨10.1016/j.bpc.2009.06.001⟩. ⟨hal-00562954⟩