Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An increased concentration of homocysteine is an important risk factor of atherosclerosis; however, the mechanism of the proatherogenic effect of this amino acid is not yet known. Studies performed during the last two decades suggest that the atherogenic effect of homocysteine may be accounted for by homocysteine thiolactone (HCTL). Homocysteine is nonspecifically activated by methionyl-tRNA synthetase; however, it is not transferred to tRNA and incorporated into proteins, but is transformed to a cyclic thioester, homocysteine thiolactone. HCTL is highly reactive and acylates free amino groups of protein lysine residues, the process referred to as protein N-homocysteinylation. Various plasma proteins are homocysteinylated in vitro and in vivo. Homocysteinylation results in the incorporation of additional thiol groups which may alter the physicochemical properties and biological activity of proteins. In particular, homocysteinylation of low-density lipoproteins (LDLs) increases their susceptibility to oxidation and accelerates their uptake by macrophages. In addition, homocysteinylated LDL elicit humoral immune response. Anti-homocysteinyllysine antibodies are detected in plasma of healthy humans and their titer is elevated in patients with ischemic heart disease or ischemic cerebral stroke. Homocysteine thiolactone is hydrolyzed to homocysteine by paraoxonase (PON), a calcium-dependent esterase synthesized in the liver and contained in plasma high-density lipoproteins (HDLs). Protein homocysteinylation may contribute to accelerated atherogenesis in individuals with hyperhomocysteinemia.
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PMID:Protein homocysteinylation: a new mechanism of atherogenesis? 1610 41

Metabolic conversion of homocysteine (Hcy) to a chemically reactive metabolite, Hcy-thiolactone, catalyzed by methionyl-tRNA synthetase is the first step in a pathway that is suggested to contribute to Hcy toxicity in humans. The accumulation of Hcy-thiolactone is detrimental because of its intrinsic ability to modify proteins by forming N-Hcy-protein adducts, in which a carboxyl group of Hcy is N-linked to the epsilon-amino group of a protein lysine residue. N-linked Hcy occurs in each protein examined and constitutes a significant pool of Hcy in the blood. N-Hcy proteins are likely to be recognized as neo-self antigens and induce an autoimmune response. Indeed, we found that autoantibodies specific for an Nepsilon-Hcy-Lys epitope on N-Hcy-proteins occur in humans. Serum levels of anti-N-Hcy-protein autoantibodies are directly correlated with plasma tHcy, but not with plasma cysteine or methionine levels. In a group of male patients with stroke, levels of anti-N-Hcy-protein autoantibodies and tHcy were significantly higher than in a group of healthy subjects. In a group of male patients with angiographically documented coronary artery disease, seropositivity for anti-N-Hcy-protein autoantibodies occurred five-fold more frequently than in controls and was an independent predictor of coronary artery disease. These findings show that the formation of N-Hcy-proteins has important physiological consequences and support a hypothesis that N-Hcy-protein is a neo-self antigen that contributes to immune activation, an important modulator of atherogenesis.
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PMID:Anti-N-homocysteinylated protein autoantibodies and cardiovascular disease. 1619 90