title: Myocilin, a component of a membrane-associated protein complex driven by a homologous Q-SNARE domain.
abstract: Myocilin is a widely expressed protein with no known function; however, mutations in myocilin appear to manifest uniquely as ocular hypertension and the blinding disease of glaucoma. Using the protein homology/analogy recognition engine (Phyre), we find that the olfactomedin domain of myocilin is similar in sequence motif and structure to a six-blade, kelch repeat motif based on the known crystal structures of such proteins. Additionally, using sequence analysis, we identify a coiled-coil segment of myocilin with homology to human Q-SNARE proteins (inset). Using COS-7 cells expressing full-length human myocilin and a version lacking the C-terminal olfactomedin domain, we identified a membrane-associated protein complex containing myocilin by hydrodynamic analysis. The myocilin construct that included the coiled-coil but lacked the olfactomedin domain formed complexes similar to the full-length protein, indicating that the coiled-coil domain of myocilin is sufficient for myocilin binding to the large detergent-resistant complex. In human retina and retinal pigment epithelium, which express myocilin, we detected the protein in a large, sodium dodecyl sulfate-resistant, membrane-associated complex. We characterized myocilin in human tissues as either a 15 S complex with an M(r) of 405000-440000 yielding a slightly elongated globular shape similar to that of known SNARE complexes or a 6.4 S dimer with an M(r) of 108000. By identifying the Q-SNARE homology within the second coil of myocilin and documenting its participation in a SNARE-like complex, we provide evidence of a SNARE domain-containing protein associated with a human disease.
authors.affiliation: Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona 85724, United States.
authors.forename: W Michael
authors.initials: WM
authors.lastname: Dismuke
authors.forename: Brian S
authors.initials: BS
authors.lastname: McKay
authors.forename: W Daniel
authors.initials: WD
authors.lastname: Stamer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000737:chemistry*; D005136:Eye Proteins / Q000096:biosynthesis / Q000737:chemistry*; D006023:Glycoproteins / Q000096:biosynthesis / Q000737:chemistry*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry; D017434:Protein Structure, Tertiary / Q000502:physiology; D050682:Q-SNARE Proteins / Q000737:chemistry* / Q000502:physiology; D040681:Structural Homology, Protein; D000099179:Myocilin
chemical_list: D003598:Cytoskeletal Proteins; D005136:Eye Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D050682:Q-SNARE Proteins; D000099179:Myocilin