title: Three-dimensional domain swapping in nitrollin, a single-domain betagamma-crystallin from Nitrosospira multiformis, controls protein conformation and stability but not dimerization.
abstract: The betagamma-crystallin superfamily has a well-characterized protein fold, with several members found in both prokaryotic and eukaryotic worlds. A majority of them contain two betagamma-crystallin domains. A few examples, such as ciona crystallin and spherulin 3a exist that represent the eukaryotic single-domain proteins of this superfamily. This study reports the high-resolution crystal structure of a single-domain betagamma-crystallin protein, nitrollin, from the ammonium-oxidizing soil bacterium Nitrosospira multiformis. The structure retains the characteristic betagamma-crystallin fold despite a very low sequence identity. The protein exhibits a unique case of homodimerization in betagamma-crystallins by employing its N-terminal extension to undergo three-dimensional (3D) domain swapping with its partner. Removal of the swapped strand results in partial loss of structure and stability but not dimerization per se as determined using gel filtration and equilibrium unfolding studies. Overall, nitrollin represents a distinct single-domain prokaryotic member that has evolved a specialized mode of dimerization hitherto unknown in the realm of betagamma-crystallins.
authors.affiliation: Center for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Hyderabad, India.
authors.forename: Penmatsa
authors.initials: P
authors.lastname: Aravind
authors.forename: Shashi Kumar
authors.initials: SK
authors.lastname: Suman
authors.forename: Amita
authors.initials: A
authors.lastname: Mishra
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Sharma
authors.forename: Rajan
authors.initials: R
authors.lastname: Sankaranarayanan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry; D017510:Protein Folding; D055503:Protein Multimerization; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D020560:Proteobacteria / Q000737:chemistry*; D013057:Spectrum Analysis; D013816:Thermodynamics; D038204:beta-Crystallins / Q000737:chemistry*; D038222:gamma-Crystallins / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D004220:Disulfides; D050505:Mutant Proteins; D021122:Protein Subunits; D038204:beta-Crystallins; D038222:gamma-Crystallins