National Center for
3SVA: Crystal structure of V57D mutant of human cystatin C
Acta Crystallogr. D Biol. Crystallogr. (2013) 69 p.577-586
Wild-type human cystatin C (hCC wt) is a low-molecular-mass protein (120 amino-acid residues, 13,343 Da) that is found in all nucleated cells. Physiologically, it functions as a potent regulator of cysteine protease activity. While the biologically active hCC wt is a monomeric protein, all crystallization efforts to date have resulted in a three-dimensional domain-swapped dimeric structure. In the recently published structure of a mutated hCC, the monomeric fold was preserved by a stabilization of the conformationally constrained loop L1 caused by a single amino-acid substitution: Val57Asn. Additional hCC mutants were obtained in order to elucidate the relationship between the stability of the L1 loop and the propensity of human cystatin C to dimerize. In one mutant Val57 was substituted by an aspartic acid residue, which is favoured in beta-turns, and in the second mutant proline, a residue known for broadening turns, was substituted for the same Val57. Here, 2.26 and 3.0 A resolution crystal structures of the V57D andV57P mutants of hCC are reported and their dimeric architecture is discussed in terms of the stabilization and destabilization effects of the introduced mutations.