Abstract
Purpose: :
To determine the regions of interaction between -crystallin subunits using computational methods and to compare this model to wide angle X-ray scattering profile.
Results: :
The secondary structure that is predicted for the -crystallin monomer subunit consists of ca. 30% β-strand and 15% -helix and contains the structural element of a β-barrel which is consistent with observations that the β-barrel is highly conserved in members of the small heat shock family of proteins. The ligand docking and dynamic simulations indicate that hydrogen bonds and hydrophobic interactions play very important roles in subunit binding. The calculated structure shows that the Trp60 residue in the -B subunit is exposed to solvent in the monomer but is buried in the dimer. This and other structural details are in agreement with experimental observations on the photo-oxidation of -crystallin (McDermott et al, Biochem. 1991). In addition, the calculated structure predicts that Lys121 of the -B subunit is located at the dimer interface which is in agreement with mass spectral data on -crystallin (Peterson et al, Mol. Vis. 2004). Wide angle X-ray scattering studies on -crystallin in solution exhibit a broad peak in the region where the scattering vector, q, has a value of 1.5 Å-1. This corresponds to an average distance of 4.9 Å between adjacent β sheets.
Conclusions: :
-crystallin is the major structural protein of the mammalian lens and has been shown to exhibit chaperone activity. A computational model and dynamics study of the -A/-B dimer is presented and the results are consistent with numerous previously reported experimental observations. In addition, the computational model is supported by wide angle X-ray scattering studies of -crystallin in solution.
Keywords: protein structure/function • anterior segment • cataract