Structure-Function Studies Of The Interactions Of The Gaseous Signaling Molecule H₂S With Myoglobin Mutants

In recent years,hydrogen sulfide(H2S)has been found to be produced endogenously in mammalian tissues,and is now known to participate in the regulation of physiological functions of physiological functions of multiple systems,including nervous,cardiovascular and endocrine systems.H2S has been proposed to be intimately associated with many diseases.Currently,endogenous H2S has been considered as the third new gaseous signaling molecule,after nitric oxide and carbon monoxide.Myoglobin(Mb)is a heme-containing protein that is present widely in mammalian tissues and organs,and binds to endogenous H2S to regulate H2S concentration in vivo.In mammals,the interaction of Mb with H2S occurs via two distinct pathways;the first is with the heme-Fe center of the Mb in forming the Mb-H2S adduct,and the second is with the porphyrin ring of the Mb heme to form the convalently modified sulfheme.These two distinct pathways have been confirmed to be affected by the structure of the Mb heme active site.This thesis will describe the preparation of several Mb mutants altering the heme active site environment using site-directed mutagenesis.UV-vis spectroscopy and X-ray crystallography were utilized to probe the interaction of different Mb mutants with H2S.The studies provided important experimental data for research on heme proteins involved in metabolism of endogenous H2S.Our results reveal that:(i)the mutation of proximal and distal histidine(His)significantly alters the structure of Mb heme active site,and thereby affects thebinding of heme Fe to H2S.and(ii)the number of hydrogen bonds in the distal cavity of the heme active site significantly affects the oxidation of Fe? to form Fe? by H2O2,which in turn affects the formation of sulfheme product.