Structural Properties of High-methionine Content Fish γ-crystallins

Tuesday, October 09, 2012 — Poster Session I
1:00 p.m. – 3:00 p.m	Natcher Conference Center, Building 45	NEI	BIOPHY-1

Authors

• Y. Chen
• H. Zhao
• P. Schuck
• G. Wistow

Abstract

Fish γ-crystallins accumulate to very high concentrations in lens cells and typically have extremely high methionine but reduced tryptophan content compared with mammalian γ-crystallins. We examined the consequences of these differences for the structural properties of zebrafish γM2a (24 Met, 1 Trp) and γM7-crystallin (16 Met, 2 Trp). γM2a was stable only up to 15mg/ml and at 0.5mg/ml began to aggregate at 45°C. γM7 could achieve at least 40mg/ml and aggregated at 50°C. For both proteins, aggregation was inhibited by αB-crystallin. Recombinant γM2a and γM7 have somewhat lower thermal stability than typical mammalian γ–crystallins. Far UV CD spectra were typical of the β-sheet structure of γ-crystallin family. Increasing concentrations of GdnHCl produced a loss of organized secondary structure, with total unfolding at 3.0 M of GdnHCl. γM7, with a pair of Trp residues in one domain, showed quenching of Trp fluorescence. γM2a, with an unpaired Trp showed enhanced fluorescence. The results confirm that paired Trp residues is required to quench UV fluorescence. By AUC, both proteins exhibited unusual behavior in solution, possibly due to low level of hydration, consistent with a very compact structure and dense packing of total crystallin content in lens fiber cells.

back to top