title: Conformational status of cytochrome c upon N-homocysteinylation: Implications to cytochrome c release.
abstract: One of the proposed mechanisms of homocysteine (Hcy) toxicity is the post-translational modification of proteins by its metabolite, homocysteine thiolactone (HTL). Incubation of proteins with HTL has been shown to form covalent adducts with ε-amino group of lysine residues of protein (called N-homocysteinylation) which ultimately results in structural and functional alterations of the modified proteins. In the present study, the effects of HTL on the conformational and heme status of cytochrome c (cyt c) were investigated. Spectroscopic analyses revealed that HTL-modified cyt c undergoes certain conformational alterations leading to disturbed heme-Trp distance and packing of the apolar groups. These alterations were accompanied with the reduction of the heme moiety and activation of peroxidase-like function of cyt c, which is known to be a crucial event for initiation of the intrinsic apoptotic pathway. Further structural characterization revealed that disruption of the heme-Met80 interaction, thereby converting the hexa-coordinate cyt c to a penta-coordinate species (with a free heme ligand), was responsible for the activation of the peroxidase activity. The study provides insights for the possible role of cyt c N-homocysteinylation in eliciting its toxicity and cell death.
authors.affiliation: Dr. B. R. Ambedkar Centre for Biomedical Research, University of Delhi, Delhi, India.
authors.forename: Gurumayum Suraj
authors.initials: GS
authors.lastname: Sharma
authors.affiliation: Dr. B. R. Ambedkar Centre for Biomedical Research, University of Delhi, Delhi, India. Electronic address: lairksingh@gmail.com.
authors.forename: Laishram Rajendrakumar
authors.initials: LR
authors.lastname: Singh
mesh_terms: D000818:Animals; D017209:Apoptosis; D002308:Cardiolipins / Q000737:chemistry; D002417:Cattle; D002942:Circular Dichroism; D045304:Cytochromes c / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry; D006710:Homocysteine / Q000031:analogs & derivatives / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008715:Methionine / Q000737:chemistry; D009206:Myocardium / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry; D009195:Peroxidase / Q000737:chemistry; D010544:Peroxidases / Q000378:metabolism; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002308:Cardiolipins; D008024:Ligands; D006710:Homocysteine; D006418:Heme; D045304:Cytochromes c; D008715:Methionine; C007957:homocysteine thiolactone; D007501:Iron; D010544:Peroxidases; D009195:Peroxidase; D010100:Oxygen
keywords: Apoptosis; Cytochrome c; EPR; N-homocysteinylation; Peroxidase; Redox state