Sequence specific 1H, 13C and 15N resonance assignments of the C-terminal domain of human S-crystallin

The high solubility and stability of crystallins present in the human eye lens maintains its transparency and refractive index with negligible protein turnover. Monomeric -crystallins and oligomeric -crystallins are made up of highly homologous double Greek key domains. These domains are symmetric and possess higher stability as a result of the complex topology of individual Greek key motifs. S-crystallin is one of the most abundant structural -crystallins present in the human eye lens. In order to understand the structural stability of individual domains of human S-crystallin in isolation vis-a-vis full length protein, we set out to structurally characterize its C-terminal domain (abbreviated hereafter as S-CTD) by solution NMR. In this direction, we have cloned, over-expressed, isolated and purified the S-CTD. The 2D [N-15-H-1] HSQC recorded with uniformly C-13/N-15 labeled S-CTD showed a highly dispersed spectrum indicating the protein to adopt an ordered conformation. In this paper, we report almost complete sequence-specific H-1, C-13 and N-15 resonance assignments of S-CTD using a suite of heteronuclear 3D NMR experiments.