Abstract
Betagamma-crystallin is a superfamily with diverse members from vertebrate lens to microbes. However, not many members have been identified and studied. Here, we report the identification of a putative exported protein from Yersinia pestis as a member of the betagamma-crystallin superfamily. Even though calcium has been known to play an important role in the physiology and virulence of the Yersinia genus, calcium-binding proteins have not yet been identified. We have studied the calcium-binding properties of two of the three crystallin domains present in this putative exported protein designated "Yersinia crystallin." These two domains (D1 and D2) have unique AA and BB types of arrangement of their Greek key motifs unlike the domains of other members of the betagamma-crystallin superfamily, which are either AB or BA types. These domains bind two calcium ions with low and high affinity-binding sites. We showed their calcium-binding properties using various probes for calcium and the effect of calcium on their secondary and tertiary structures. Although both domains bind calcium, D1 underwent drastic changes in secondary and tertiary structure and hydrodynamic volume upon calcium binding. Domain D1, which is intrinsically unstructured in the apo form, requires calcium for the typical betagamma-crystallin fold. Calcium exerted an extrinsic stabilization effect on domain D1 but not on D2, which is also largely unstructured. We suggest that this protein might be involved in calcium-dependent processes, such as stress response or physiology in the Yersinia genus, similar to its microbial relatives and mammalian lens crystallins.
Highlights
Crystallins are the major structural proteins of the lens
Calcium exerted an extrinsic stabilization effect on domain D1 but not on D2, which is largely unstructured. We suggest that this protein might be involved in calcium-dependent processes, such as stress response or physiology in the Yersinia genus, similar to its microbial relatives and mammalian lens crystallins
We identified six Greek key motifs in their N-terminal ends organized as three ␥-crystallin domains
Summary
The calcium-binding microbial homologous of crystallins, if any, in Y. pestis, with analogy to microbial ␥-crystallins, could be a possible candidate for stress response encountered during the various phases of the life cycle in animals and humans. We searched the genome sequence of Y. pestis CO92 and found a putative exported protein (locus tag YPO2884) and a hypothetical protein (locus tag YPO0466) as microbial relatives of ␥-crystallins, containing three and two ␥ domains, respectively. In this context, we studied two of the three ␥-crystallin domains present in the sequence of a putative exported protein, which we refer to as “Yersinia crystallin.”. Our data showed that domains of Yersinia crystallin bind calcium with micromolar affinity. We report the presence of a homologue and a paralogue of Yersinia crystallin that we have identified in this pathogen and another microorganism
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