Conformational heterogeneity and dynamics in a βγ-crystallin from Hahella chejuensis

Most of the βγ-crystallins are structural proteins with high intrinsic stability, which gets enhanced by Ca(2+)-binding in microbial members. Functions of most of these proteins are yet to be known. However, a few of them were reported to be involved in Ca(2+)-dependent and stress-related functions. Hahellin, a microbial homolog, is a natively unfolded protein that acquires a well-folded structure upon Ca(2+) binding. Although the structure of βγ-crystallin domains is well understood, the dynamical features are yet to be explored. We have investigated for the first time the equilibrium dynamics, conformational heterogeneity and associated low-lying free-energy states of hahellin in its Ca(2+)-bound form using NMR spectroscopy to understand the dynamics of a βγ-crystallin domain. Hahellin shows large conformational heterogeneity with nearly 40% of the residues, some of which are part of Ca(2+)-binding loops, accessing alternative states. Further, out of the two Greek key motifs, which together constitute the βγ-crystallin domain, the second Greek key motif is floppy as compared to its relatively rigid counterpart. Taken together, we believe that these characteristics might be of importance to understand the stability and functions of βγ-crystallin domains.