Molecular Bases of Disease
The pattern of apolipoprotein A-I lysine carbamylation reflects its lipidation state and the chemical environment within human atherosclerotic aorta
Protein lysine carbamylation is an irreversible post-translational modification resulting in generation of homocitrulline (N-ε-carbamyllysine), which no longer possesses a charged ε-amino moiety. Two distinct pathways can promote protein carbamylation. One results from urea decomposition, forming an equilibrium mixture of cyanate (CNO−) and the reactive electrophile isocyanate. The second pathway involves myeloperoxidase (MPO)-catalyzed oxidation of thiocyanate (SCN−), yielding CNO− and isocyanate.Site-specific 5-hydroxytryptophan incorporation into apolipoprotein A-I impairs cholesterol efflux activity and high-density lipoprotein biogenesis
Apolipoprotein A-I (apoA-I) is the major protein constituent of high-density lipoprotein (HDL) and a target of myeloperoxidase-dependent oxidation in the artery wall. In atherosclerotic lesions, apoA-I exhibits marked oxidative modifications at multiple sites, including Trp72. Site-specific mutagenesis studies have suggested, but have not conclusively shown, that oxidative modification of Trp72 of apoA-I impairs many atheroprotective properties of this lipoprotein. Herein, we used genetic code expansion technology with an engineered Saccharomyces cerevisiae tryptophanyl tRNA-synthetase (Trp-RS):suppressor tRNA pair to insert the noncanonical amino acid 5-hydroxytryptophan (5-OHTrp) at position 72 in recombinant human apoA-I and confirmed site-specific incorporation utilizing MS.
