Complement Factor H, Vitronectin, and Opticin Are Tyrosine-Sulfated Proteins of the Retinal Pigment Epithelium

Abstract

Lack of tyrosine sulfation of ocular proteins results in disorganized photoreceptor structure and drastically reduced visual function, demonstrating the importance of this post-translational modification to vision. To understand the role that tyrosine sulfation plays in the function of ocular proteins, we identified some tyrosine-sulfated proteins in the retinal pigment epithelium using two independent methods, immuno-affinity column purification with an anti-sulfotyrosine specific antibody and computer-based sequence analysis of retinal pigment epithelium secretome by means of the prediction program Sulfinator. Radioactive labeling followed by thin layer electrophoresis revealed that three proteins, vitronectin, opticin, and complement factor H (CFH), were post-translationally modified by tyrosine sulfation. The identification of vitronectin and CFH as tyrosine-sulfated proteins is significant, since both are deposited in drusen in the eyes of patients with age-related macular degeneration (AMD). Furthermore, mutations in CFH have been determined to be a major risk factor in the development of AMD. Future studies that seek to understand the role of CFH in the development of AMD should take into account the role that tyrosine sulfation plays in the interaction of this protein with its partners, and examine whether modulating sulfation provides a potential therapeutic target.

Post-translational modifications and their applications in eye research

“…In addition, profiling of the secretome in bovine RPE demonstrated the presence of three tyrosine-sulfated proteins. This included tyrosine-sulfated complement factor H, which may be involved in age-associated macular degeneration (202). Following H 2 O 2 challenge, a novel 45 kDa truncated modification on the retinoid isomerohydrolase (RPE65) protein was identified by LC-MS/MS in murine RPE, suggesting that the RPE65 cleavage process may be affected by oxidative stress (203).…”

Role of tyrosine-sulfated proteins in retinal structure and function

“…As initial steps towards that goal, extracts of bovine RPE and neurosensory retina were subjected to immunoaffinity column purification using the PSG2 antibody (Kanan et al 2014a, 2014b). Three proteins, fibulin 2, vitronectin, and opticin, were identified (Kanan et al 2014a, 2014b).…”

“…As initial steps towards that goal, extracts of bovine RPE and neurosensory retina were subjected to immunoaffinity column purification using the PSG2 antibody (Kanan et al 2014a, 2014b). Three proteins, fibulin 2, vitronectin, and opticin, were identified (Kanan et al 2014a, 2014b). In addition, data mining and tyrosine sulfation prediction analysis of the RPE secretome identified complement factor H (CFH) as another tyrosinesulfated protein (Kanan et al 2014b).…”

“…Three proteins, fibulin 2, vitronectin, and opticin, were identified (Kanan et al 2014a, 2014b). In addition, data mining and tyrosine sulfation prediction analysis of the RPE secretome identified complement factor H (CFH) as another tyrosinesulfated protein (Kanan et al 2014b). Further in vivo and in vitro analysis confirmed that all four proteins are tyrosine-sulfated (Kanan et al 2014a, 2014b).…”

“…Opticin is another tyrosine-sulfated protein (Kanan et al 2014b). This protein has recently been shown to prevent neovascularization in the oxygen-induced retinopathy model (OIR model) in mouse eyes (Le Goff et al 2012a).…”