Gamma S-crystallin of bovine and human eye lens: solution structure, stability and folding of the intact two-domain protein and its separate domains

The X-ray Crystal Structure of Human γS-crystallin C-terminal Domain

“…The HGSC eluted at 15.3 ml, over a wide range of protein concentration application (0.2-6.5 mg/ml) at both pH 6.5 and 8.0. For comparison, full-length bovine ␥S-crystallin at pH 8.0 elutes at 14.4 ml, in agreement with the monomeric nature of the C-terminal domain of human ␥S in solution, as determined using ultracentrifugation (19).…”

“…The recreation of these 2-fold interactions between single domains underscores the idea that domain pairing is an ancestral dimer trait. However, without the covalent linker, the local concentration of a single domain is insufficient to form a dimer in solution (19). The weakness of the interface interaction renders it susceptible to deformation, and it is the first likely hydrophobic surface to become water exposed during denaturation, in line with computer simulated unfolding studies of ␥B-crystallin (20).…”

“…Now that the new conformation has been seen in a ␥S-crystallin in a different lattice, it is likely to be independent of a secondary lattice effect. It will be interesting to ascertain whether this new conformation contributes to the lower stability of ␥S-crystallin toward denaturants compared with ␥B-crystallin (19) and/or affects the folding.…”

“…␥S-crystallin is a major structural protein in the human eye lens (18). Human and bovine ␥S-crystallins and their isolated domains are very stable and show two-state unfolding, allowing detailed quantitative thermodynamic properties of the proteins to be evaluated (19). Computer simulations of heat-induced unfolding of bovine ␥B-crystallin also indicate high stability and furthermore suggest that the first stage of unfolding involves the dissociation of the paired domains (20).…”

Biophysical chemistry of the ageing eye lens

“…Due to its chromatographic properties, γS-crystallin was originally classified as a β-crystallin (βS), but, once the genetic sequence of the crystallins was understood, it was re-classified as an early evolutionary offshoot of the γ-crystallins ( Quax-Jeuken et al 1985;Smith et al 1995). The sequence of γS-crystallin is highly conserved throughout all vertebrates and is regarded as one of the more important proteins in the lens structure (Bloemendal et al 2004;Wenk et al 2000). The crystallisation of human γS-crystallin has yet to be achieved, but a structure determined by NMR spectroscopy is available (Kingsley et al 2013).…”