Mass spectrometry-based characterization of the vitreous phosphoproteome

Purpose: The vitreous gel is a highly hydrated extracellular matrix containing many proteins. These proteins are likely accumulated in the vitreous by local secretion, filtration from the blood, or diffusion from the surrounding tissues and vasculature, and may be altered in disease state. In the last several years, several reports of large-scale profiling of vitreous proteins have been published; however, there is little information on the characterization of the phosphoproteome of vitreous. Here, we sought to identify phosphopeptides and their phosphorylation sites from vitreous.Experimental design: We used titanium dioxide (TiO₂) to enrich phosphopeptides from vitreous and identified them by LC-MS/MS.Results: We identified 85 unique phosphopeptides and the phosphorylation sites from 44 proteins.Conclusions and clinical relevance: We present a method for characterization of phosphoproteome from vitreous samples using current MS technologies and yielded an initial assessment of the phosphoprotein/peptide content of human vitreous, thus providing important biological information toward further understanding of the post-translational modifications of vitreous proteins and their functional significance in disease.