Three‐dimensional model and quaternary structure of the human eye lens protein γS‐crystallin based on β‐ and γ‐crystallin X‐ray coordinates and ultracentrifugation

Abstract

A 3-dimensional model of the human eye lens protein yS-crystallin has been constructed using comparative modeling approaches encoded in the program COMPOSER on the basis of the 3-dimensional structure of y-crystallin and 0-crystallin. The model is biased toward the monomeric yB-crystallin, which is more similar in sequence. Bovine yS-crystallin was shown to be monomeric by analytical ultracentrifugation without any tendency to form assemblies up to concentrations in the millimolar range. The connecting peptide between domains was therefore built assuming an intramolecular association as in the monomeric y-crystallins. Because the linker has 1 extra residue compared with yB and PB2, the conformation of the connecting peptide was constructed by using a fragment from a protein database. yS-crystallin differs from yB-crystallin mainly in the interface region between domains. The charged residues are generally paired, although in a different way from both 0-and y-crystallins, and may contribute to the different roles of these proteins in the lens.

Association Behaviour of Human βB1-Crystallin and its Truncated Forms

“…The protein eluted as a narrow, symmetrical peak on gel ®ltration [ Fig. 2(c)], with an identical elution volume as calf lens bB2-crystallin that has previously been well characterized as a dimer (Zarina et al, 1994). Furthermore, human bB2-crystallin eluted at the same position over a broad protein concentration range, showing no evidence of higher-order solution interactions at higher protein concentrations (Fig.…”

“…Both human and bovine bB2-crystallin behave as monodisperse dimers on light scattering over a broad range of protein concentrations, in agreement with their close sequence identity of 97 %. Both human and bovine bB2-crystallin gave slightly low estimates of M r from size exclusion chromatography as compared with light scattering and ultracentrifugation data (Zarina et al, 1994), which probably indicates a slight interaction between the bB2-dimers and the column matrix, rather than re¯ecting the equilibrium distribution between monomer and dimer.…”

“…In bovine lens these are named in order of size bH-, bL1-and bL2-crystallin, with the latter being mainly comprised of bB2-crystallin dimer (Bindels, Koppers and Hoenders, 1981;Slingsby and Bateman, 1990;Zarina et al, 1994). Separation of these three fractions is sensitive to buffer conditions and bH-crystallin exhibits a concentration dependent equilibrium with smaller oligomers (Siezen, Anello and Thomson, 1986;Bateman and Slingsby, 1992).…”

Deamidation of Human βB1 Alters the Elongated Structure of the Dimer

“…7 S determined for wt bB1 was less than the s-value of 4 . 2 S previously determined for bB2 (Zarina et al, 1994) or 3 . 7 S for bovine bL2 at similar concentrations and molecular weights (Bindels et al, 1981).…”

Specific Glutamine and Asparagine Residues of γ-S Crystallin Are Resistant to in Vivo Deamidation

“…Analysis of the extent of deamidation of peptides and proteins has established that secondary protein structure (8), as well as the primary sequence near the asparagine residue (9), may determine the lability toward deamidation. ␥-S protein from aged human lens should provide an ideal system to study the effects of protein structure upon deamidation, because much is known about the three-dimensional structure of this polypeptide (10). Molecular modeling of this protein has suggested that glutamine 92, glutamine 96, asparagine 143, and glutamine 170 are all solvent-exposed.…”