A distinctive histidine residue is essential for in vivo glycation-inactivation of human CD59 transgenically expressed in mice erythrocytes: Implications for human diabetes complications

摘要

Clinical and experimental evidences support a link between the complement system and the pathogenesis of diabetes complications. CD59, an extracellular cell membrane-anchored protein, inhibits formation of the membrane attack complex (MAC), the main effector of complement-mediated tissue damage. This complement regulatory activity of human CD59 (hCD59) is inhibited by hyperglycemia-induced epsilon-amino glycation of Lys(41). Biochemical and structural analyses of glycated proteins with known three-dimensional structure revealed that glycation of -amino lysyl residues occurs predominantly at "glycation motives" that include lysyl/lysyl pairs or proximity of a histidyl residue, in which the imidazolyl moiety is approximate to 5 angstrom from the -amino group. hCD59 contains a distinctive Lys(41)/His(44) putative glycation motif within its active site. In a model of transgenic diabetic mice expressing in erythrocytes either the wild type or a H44Q mutant form of hCD59, we demonstrate in vivo that the His(44) is required for Lys(41) glycation and consequent functional inactivation of hCD59, as evidenced using a mouse erythrocytes hemolytic assay. Since (1) the His(44) residue is not present in CD59 from other animal species and (2) humans are particularly prone to develop complications of diabetes, our results indicate that the Lys(41)/His(44) glycation motif in human CD59 may confer humans a higher risk of developing vascular disease in response to hyperglycemia.