Amyloid fibril formation by the glaucoma-associated olfactomedin domain of myocilin

J Mol Biol. 2012 Aug 10;421(2-3):242-55. doi: 10.1016/j.jmb.2011.12.016. Epub 2011 Dec 13.

Abstract

Myocilin is a protein found in the extracellular matrix of trabecular meshwork tissue, the anatomical region of the eye involved in regulating intraocular pressure. Wild-type (WT) myocilin has been associated with steroid-induced glaucoma, and variants of myocilin have been linked to early-onset inherited glaucoma. Elevated levels and aggregation of myocilin hasten increased intraocular pressure and glaucoma-characteristic vision loss due to irreversible damage to the optic nerve. In spite of reports on the intracellular accumulation of mutant and WT myocilin in vitro, cell culture, and model organisms, these aggregates have not been structurally characterized. In this work, we provide biophysical evidence for the hallmarks of amyloid fibrils in aggregated forms of WT and mutant myocilin localized to the C-terminal olfactomedin (OLF) domain. These fibrils are grown under a variety of conditions in a nucleation-dependent and self-propagating manner. Protofibrillar oligomers and mature amyloid fibrils are observed in vitro. Full-length mutant myocilin expressed in mammalian cells forms intracellular amyloid-containing aggregates as well. Taken together, this work provides new insights into and raises new questions about the molecular properties of the highly conserved OLF domain, and suggests a novel protein-based hypothesis for glaucoma pathogenesis for further testing in a clinical setting.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Amyloid / biosynthesis*
  • Biophysics
  • Cytoskeletal Proteins / chemistry
  • Cytoskeletal Proteins / metabolism*
  • Escherichia coli / metabolism
  • Extracellular Matrix Proteins / metabolism*
  • Eye Proteins / chemistry
  • Eye Proteins / metabolism*
  • Glaucoma / metabolism*
  • Glycoproteins / chemistry
  • Glycoproteins / metabolism*
  • Humans
  • Molecular Sequence Data
  • Sequence Homology, Amino Acid

Substances

  • Amyloid
  • Cytoskeletal Proteins
  • Extracellular Matrix Proteins
  • Eye Proteins
  • Glycoproteins
  • olfactomedin
  • trabecular meshwork-induced glucocorticoid response protein