The stability of myocilin olfactomedin domain variants provides new insight into glaucoma as a protein misfolding disorder

Biochemistry. 2011 Jul 5;50(26):5824-33. doi: 10.1021/bi200231x. Epub 2011 Jun 9.

Abstract

Myocilin variants, localized to the olfactomedin (OLF) domain, are linked to early-onset, inherited forms of open-angle glaucoma. Disease-causing myocilin variants accumulate within trabecular meshwork cells instead of being secreted to the trabecular extracellular matrix of the eye. We hypothesize that, like in other diseases of protein misfolding, aggregation and downstream pathogenesis originate from the compromised thermal stability of mutant myocilins. In an expansion of our pilot study of four mutants, we compare 21 additional purified OLF variants by using a fluorescence stability assay and investigate the secondary structure of the most stable variants by circular dichroism. Variants with lower melting temperatures are correlated with earlier glaucoma diagnoses. The chemical chaperone trimethylamine N-oxide is capable of restoring the stability of most, but not all, variants to wild-type (WT) levels. Interestingly, three reported OLF disease variants, A427T, G246R, and A445V, exhibited properties indistinguishable from those of WT OLF, but an increased apparent aggregation propensity in vitro relative to that of WT OLF suggests that biophysical factors other than thermal stability, such as kinetics and unfolding pathways, may also be involved in myocilin glaucoma pathogenesis. Similarly, no changes from WT OLF stability and secondary structure were detected for three annotated single-nucleotide polymorphism variants. Our work provides the first quantitative demonstration of compromised stability among many identified OLF variants and places myocilin glaucoma in the context of other diseases of protein misfolding.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • Cytoskeletal Proteins / chemistry*
  • Cytoskeletal Proteins / genetics*
  • Cytoskeletal Proteins / metabolism
  • Extracellular Matrix Proteins / chemistry*
  • Eye Proteins / chemistry*
  • Eye Proteins / genetics*
  • Eye Proteins / metabolism
  • Glaucoma / genetics
  • Glaucoma / metabolism*
  • Glycoproteins / chemistry*
  • Glycoproteins / genetics*
  • Glycoproteins / metabolism
  • Humans
  • Mice
  • Molecular Sequence Data
  • Mutation*
  • Protein Stability
  • Protein Structure, Tertiary
  • Proteostasis Deficiencies / genetics
  • Proteostasis Deficiencies / metabolism*
  • Rats

Substances

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