The pattern of apolipoprotein A-I lysine carbamylation as a probe of the environment within human atherosclerotic aorta

ABSTRACT: Protein lysine residue carbamylation is an irreversible post-translational modification, resulting in the generation of protein-bound homocitrulline (N--carbamyllysine). Carbamylation alters protein structure and can thus also alter protein function because of the loss of the charged -amino lysine moiety. Two distinct pathways can promote protein carbamylation. The first pathway occurs as a result of urea decomposition forming an equilibrium mixture of cyanate (CNO-) and the reactive electrophile isocyanate; the second (enzymatic) pathway occurs from myeloperoxidase (MPO)–catalyzed oxidation of thiocyanate (SCN-), yielding CNO- and isocyanate. We and others have previously shown that apolipoprotein A-I (apoA-I), the major protein constituent of high density lipoprotein (HDL), is a target for MPO-catalyzed modification in vivo altering its function, converting the traditionally cardio-protective lipoprotein into a pro-atherogenic and pro-apoptotic one. We hypothesized that insights into the chemical environment within the human artery wall could be gained by monitoring site-specific carbamylation patterns of apoA-I recovered from human atherosclerotic aorta. Toward testing this hypothesis, we first mapped and quantified carbamyllysine obtained from in vitro carbamylation of apoA-I by: (i) the urea driven (cyanate) vs. the inflammatory driven (MPO) pathways; as well as (ii) in lipid-poor vs. lipidated apoA-I (reconstituted nascent HDL). Our in vitro studies, interpreted in the context of existing structural models, suggest lysine residues within regional proximity of the known MPO binding sites on HDL are preferentially targeted by the enzymatic (MPO) carbamylation pathway, whereas the non-enzymatic (cyanate) pathway leads to nearly uniform distribution of carbamylated lysine residues along the apoA-I polypeptide chain. Quantitative proteomic analyses of apoA-I recovered from human aortic atheroma identified 16 of the 21 total lysine residues as carbamylated and suggests that the majority of apoA-I carbamylation in vivo occurs via the non-enzymatic cyanate pathway, and on ‘lipid-poor’ apoA-I forms. Monitoring the patterns of post translational modification of apoA-I lysine residues in vivo can provide insights into the chemical environment within human atheroma.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Heart

DISEASE(S): Cardiovascular System Disease

SUBMITTER: Shawna battle  

LAB HEAD: Stanley Hazen

PROVIDER: PXD027881 | Pride | 2022-04-06

REPOSITORIES: Pride