This mouse will be the ideal model with which to better understand the role that tyrosine sulfation plays in the function of CFH in complement regulation. Due to the involvement of tyrosine sulfation in protein-protein interactions , , using the PSG2 immunoaffinity column to isolate tyrosine em O /em -sulfated proteins would not only pull down tyrosine-sulfated proteins, but also nonsulfated proteins which may be co-purifying due to their direct or indirect interaction with tyrosine-sulfated proteins. 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 Prifuroline 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. Introduction Tyrosine sulfation, a post-translational modification employed in higher eukaryotes , is catalyzed by two Type II transmembrane enzymes, tyrosylprotein sulfotransferases 1 & 2 (TPST 1 & 2). It was initially described by Bettelheim in 1954, but was later found to be a common post-translational modification , . Tyrosine sulfation occurs in the trans-Golgi compartment and requires 3-phosphoadenosine 5-phosphosulfate (PAPS) as a sulfate donor for the reaction . It is only observed on secreted and transmembrane proteins: nuclear and cytoplasmic proteins have not been reported to have this modification , . However, the role of tyrosine sulfation in protein function has only recently been investigated C. Initial analyses of the amino acid sequences surrounding the identified sulfated tyrosines showed a predominance of acidic amino acids within 5 residues surrounding the sulfated tyrosines . However, later studies showed that some tyrosine-sulfated proteins do not follow these criteria, and it is the secondary structure that may expose the tyrosine residue to a TPST to be sulfated . Mouse models that lack either or both TPST enzymes exhibit distinctly different phenotypes C. Mice lacking Rabbit Polyclonal to AKT1/2/3 (phospho-Tyr315/316/312) both TPSTs show the most drastic phenotype Prifuroline of cardio-pulmonary insufficiency and subsequent death within 2 months after birth . Previous studies have demonstrated that these animals also display ocular defects , . The studies. Recombinant CFH was immunoprecipitated from the media of human CFH-transfected HEK293T cells. One portion was subjected to PNGase F treatment while another was left untreated. Immunoblot analysis showed a size decrease with PNGase F treatment (Figure 5B). Both the PNGase F-treated and untreated immunoprecipitants were recognized by PSG2, with the PSG2 showing better reactivity to the PNGase F- treated immunoprecipitant (compare lane 2 to 1 1, Figure 5B). metabolic labeling with 35S showed that CFH incorporated the label (Figure 5C). PNGase F treatment eliminated 75% of 35S radioactivity as determined by densitometry (Figure 5C). This suggests that the N-glycosylated residues on CFH are also sulfated, which is in agreement with a previous report . Barium hydroxide hydrolysis and TLE showed that the remaining 25% of label on CFH is on tyrosine(s), as indicated by the co-localization of the radioactive tyrosine sulfate from radioactive CFH with the non-radioactive tyrosine sulfate standard (Figure 5D). Discussion Previous studies using the and comparisons of wild-type and opticin knockout animals in the oxygen-induced retinopathy model of neovascularization showed more neovascularization in the knockout animal . These results were further examined em in vitro /em , in which it was shown that opticin binds collagen and thereby inhibits endothelial cell integrins (1)(1) and (2)(1) from binding collagen, a necessity for pro-angiogenic signaling . It has also been shown that opticin can bind retinal growth hormone (GH) in chick embryonic vitreous humor . It would be interesting to see if removing sulfation on opticin modulates its interaction with collagen or GH and if it affects anti-angiogenic functions. Vitronectin has been previously shown to be tyrosine-sulfated in human plasma . Its tyrosine-sulfated residues were identified as Tyr-75 and Tyr-78 . These two residues are close to the RGD Prifuroline cell attachment site on the protein, which resides between residues 64C66. The RGD sites on vitronectin have been previously shown to bind integrin receptor v3 and v5 , . However, for this to occur, the RGD site must be exposed to the surface, which can be influenced by type of surrounding residues. For example, the presence of a proline residue that follows the RGD site silences the motif by preventing surface accessibility . Therefore, the function of tyrosine sulfation, due to its hydrophilic nature and close proximity to the RGD site, may be to expose the RGD domain at the surface of the protein, facilitating its interaction with integrin receptors on cells. Since tyrosine sulfation has been shown to be necessary for protein-protein interactions , C, the presence of a highly charged sulfate group may facilitate the interaction of vitronectin with a positively charged domain(s) on an interacting partner..