Protein Covalent Modification by Homocysteine: Consequences and Clinical Implications

Abstract Posttranslational modifications (PTMs) generally refer to the incorporation of functional groups at specific residues or proteolysis of regulatory subunits, and also the folding processes, en route to attain a final folded functional protein. A vast majority of proteins have to undergo certain posttranslational modifications to attain their final functional states. An adequate number of proteins undergoing PTMs are now easily detected in neurodegenerative diseases (NDs) tissues; thus, they are considered to be another defining feature of the molecular pathology in neurodegenerative conditions. Recently increased levels of homocysteine (Hcy) have been shown to be involved in several pathological conditions, including cardiovascular complications and neurodegeneration. One defining characteristic feature of elevated Hcy levels is the modification of cellular and serum proteins with Hcy and its metabolite homocysteine thiolactone (HTL), a process known as protein homocysteinylation. Thus, protein homocysteinylation has been identified as the key player in determining the progression of Hcy-associated clinical manifestations. This chapter describes the structural and functional consequences of posttranslational protein modification via homocysteinylation, and its association with human diseases. Major clinical complications of elevated Hcy are also discussed. We discuss the recent advances and the widely used strategies achieved toward the treatment of hyperhomocysteinemia. This chapter may provide insights into the pathological consequences of hyperhomocysteinemia.