The glaucoma-associated olfactomedin domain of myocilin is a novel calcium binding protein.

TitleThe glaucoma-associated olfactomedin domain of myocilin is a novel calcium binding protein.
Publication TypeJournal Article
Year of Publication2012
AuthorsDonegan, RK, Hill, SE, Turnage, KC, Orwig, SD, Lieberman, RL
JournalJ Biol Chem
Volume287
Issue52
Pagination43370-7
Date Published2012 Dec 21
ISSN1083-351X
KeywordsAnimals, Calcium-Binding Proteins, Cattle, Cytoskeletal Proteins, Extracellular Matrix Proteins, Eye Proteins, Glaucoma, Glycoproteins, Humans, Hydrogen-Ion Concentration, Intraocular Pressure, Mice, Mutation, Protein Structure, Tertiary, Swine, Trabecular Meshwork
Abstract

Myocilin is a protein found in the trabecular meshwork extracellular matrix tissue of the eye that plays a role in regulating intraocular pressure. Both wild-type and certain myocilin variants containing mutations in the olfactomedin (OLF) domain are linked to the optic neuropathy glaucoma. Because calcium ions are important biological cofactors that play numerous roles in extracellular matrix proteins, we examined the calcium binding properties of the myocilin OLF domain (myoc-OLF). Our study reveals an unprecedented high affinity calcium binding site within myoc-OLF. The calcium ion remains bound to wild-type OLF at neutral and acidic pH. A glaucoma-causing OLF variant, myoc-OLF(D380A), is calcium-depleted. Key differences in secondary and tertiary structure between myoc-OLF(D380A) and wild-type myoc-OLF, as well as limited access to chelators, indicate that the calcium binding site is largely buried in the interior of the protein. Analysis of six conserved aspartate or glutamate residues and an additional 18 disease-causing variants revealed two other candidate residues that may be involved in calcium coordination. Our finding expands our knowledge of calcium binding in extracellular matrix proteins; provides new clues into domain structure, function, and pathogenesis for myocilin; and offers insights into highly conserved, biomedically relevant OLF domains.

DOI10.1074/jbc.M112.408906
Alternate JournalJ. Biol. Chem.
PubMed ID23129764
PubMed Central IDPMC3527924
Grant ListR01 EY021205 / EY / NEI NIH HHS / United States
R01EY021205 / EY / NEI NIH HHS / United States