Sequence specific 1H, 13C and 15N resonance assignments of the C-terminal domain of human γS-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 γ-crystallins and oligomeric β-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. γS-crystallin is one of the most abundant structural βγ-crystallins present in the human eye lens. In order to understand the structural stability of individual domains of human γS-crystallin in isolation vis-à-vis full length protein, we set out to structurally characterize its C-terminal domain (abbreviated hereafter as γS-CTD) by solution NMR. In this direction, we have cloned, over-expressed, isolated and purified the γS-CTD. The 2D [15N-1H] HSQC recorded with uniformly 13C/15N labeled γS-CTD showed a highly dispersed spectrum indicating the protein to adopt an ordered conformation. In this paper, we report almost complete sequence-specific 1H, 13C and 15N resonance assignments of γS-CTD using a suite of heteronuclear 3D NMR experiments.