Association properties and unfolding of a βγ-crystallin domain of a Vibrio-specific protein.
The βγ-crystallin superfamily possesses a large number of versatile members, of which only a few members other than lens βγ-crystallins have been studied. Understanding the non-crystallin functions as well as origin of crystallin-like properties of such proteins is possible by exploring novel members from diverse sources. We describe a novel βγ-crystallin domain with S-type (Spherulin 3a type) Greek key motifs in protein vibrillin from a pathogenic bacterium Vibrio cholerae. This domain is a part of a large Vibrio-specific protein prevalent in Vibrio species (found in at least fourteen different strains sequenced so far). The domain contains two canonical N/D-N/D-X-X-S/T-S Ca(2+)-binding motifs, and bind Ca(2+). Unlike spherulin 3a and other microbial homologues studied so far, βγ-crystallin domain of vibrillin self-associates forming oligomers of various sizes including dimers. The fractionated dimers readily form octamers in concentration-dependent manner, suggesting an association between these two major forms. The domain associates/dissociates forming dimers at the cost of monomeric populations in the presence of Ca(2+). No such effect of Ca(2+) has been observed in oligomeric species. The equilibrium unfolding of both forms follows a similar pattern, with the formation of an unfolding intermediate at sub-molar concentrations of denaturant. These properties exhibited by this βγ-crystallin domain are not shown by any other domain studied so far, demonstrating the diversity in domain properties.
Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad, India.
Shashi Kumar
SK
Suman
Daddali
D
Ravindra
Yogendra
Y
Sharma
Amita
A
Mishra
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D013045:Species Specificity; D013696:Temperature; D014734:Vibrio cholerae; D038204:beta-Crystallins / Q000737:chemistry*; D038222:gamma-Crystallins / Q000737:chemistry*
D001426:Bacterial Proteins; D038204:beta-Crystallins; D038222:gamma-Crystallins; D002118:Calcium