Proteomic analysis of human very low-density lipoprotein by two-dimensional gel electrophoresis and MALDI-TOF/TOF

Biochemical studies of lipoproteins have shed light on their composition, highly contributing to the comprehension of their function. Due to the complexity of their structure, however, an in-depth structural analysis, in terms of components and PTMs, may still unravel important players in physiological and pathological processes of lipid metabolism. In this study, we performed a protein map of very low-density lipoprotein (VLDL) using a 2-DE MALDI-TOF/TOF proteomic approach. Several VLDL-associated apolipoproteins were identified, including five isoforms of apoE, three isoforms of apoC-IV, and one isoform each of apoC-III, apoM, apoA-I, and apoA-IV. Notably, we also identified seven isoforms of apoL-I and two isoforms of prenylcysteine Iyase as new VLDL-associated proteins. Furthermore, we were able to identify PTM of apoE, which was found to be differently O-glycosylated at Thr(212) residue, and PTM of apol-I which we described, for the first time, to be phosphorylated at Ser(296). While the physiological relevance of our finding remains to be assessed, we believe that our results will be useful as reference for future studies of VLDL structure in specific physiopathological conditions.