Computational design and biophysical characterization of aggregation-resistant point mutations for γD crystallin illustrate a balance of conformational stability and intrinsic aggregation propensity

Biochemistry. 2011 Feb 8;50(5):628-39. doi: 10.1021/bi100978r. Epub 2011 Jan 13.

Abstract

γD crystallin is a natively monomeric eye-lens protein that is associated with hereditary juvenile cataract formation. It is an attractive model system as a multidomain Greek-key protein that aggregates through partially folded intermediates. Point mutations M69Q and S130P were used to test (1) whether the protein-design algorithm RosettaDesign would successfully predict mutants that are resistant to aggregation when combined with informatic sequence-based predictors of peptide aggregation propensity and (2) how the mutations affected relative unfolding free energies (ΔΔG(un)) and intrinsic aggregation propensity (IAP). M69Q was predicted to have ΔΔG(un) ≫ 0, without significantly affecting IAP. S130P was predicted to have ΔΔG(un) ∼ 0 but with reduced IAP. The stability, conformation, and aggregation kinetics in acidic solution were experimentally characterized and compared for the variants and wild-type (WT) protein using circular dichroism and intrinsic fluorescence spectroscopy, calorimetric and chemical unfolding, thioflavin-T binding, chromatography, static laser light scattering, and kinetic modeling. Monomer secondary and tertiary structures of both variants were indistinguishable from WT, while ΔΔG(un) > 0 for M69Q and ΔΔG(un) < 0 for S130P. Surprisingly, despite being the least conformationally stable, S130P was the most resistant to aggregation, indicating a significant decrease of its IAP compared to WT and M69Q.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Circular Dichroism
  • Computer-Aided Design
  • Humans
  • Kinetics
  • Molecular Sequence Data
  • Point Mutation*
  • Protein Conformation
  • Protein Folding
  • Protein Stability
  • Thermodynamics
  • gamma-Crystallins / chemistry*
  • gamma-Crystallins / genetics*
  • gamma-Crystallins / metabolism

Substances

  • CRYGD protein, human
  • gamma-Crystallins