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Ice-binding proteins (IBPs) inhibit ice growth through direct interaction with ice crystals to permit the survival of polar organisms in extremely cold environments. FfIBP is an ice-binding protein encoded by the Antarctic bacterium Flavobacterium frigoris PS1. The X-ray crystal structure of FfIBP was determined to 2.1 Å resolution to gain insight into its ice- binding mechanism. The refined structure of FfIBP shows an intramolecular disulfide bond, and analytical ultracentrifugation and analytical size-exclusion chromatography show that it behaves as a monomer in solution. Sequence alignments and structural comparisons of IBPs allowed two groups of IBPs to be defined, depending on sequence differences between the α2 and 4 loop regions and the presence of the disulfide bond. Although FfIBP closely resembles Leucosporidium (recently re-classified as Glaciozyma) IBP (LeIBP) in its amino-acid sequence, the thermal hysteresis (TH) activity of FfIBP appears to be tenfold higher than that of LeIBP. A comparison of the FfIBP and LeIBP structures reveals that FfIBP has different ice-binding residues as well as a greater surface area in the ice-binding site. Notably, the ice-binding site of FfIBP is composed of a T-A/G-X-T/N motif, which is similar to the ice-binding residues of hyperactive antifreeze proteins. Thus, it is proposed that the difference in TH activity between FfIBP and LeIBP may arise from the amino-acid composition of the ice-binding site, which correlates with differences in affinity and surface complementarity to the ice crystal. In conclusion, this study provides a molecular basis for understanding the antifreeze mechanism of FfIBP and provides new insights into the reasons for the higher TH activity of FfIBP compared with LeIBP. [ABSTRACT FROM AUTHOR]

Shank proteins are a new family of scaffold proteins interacting with various membrane and cytoplasmic proteins. Shank contains multiple protein-protein interaction sites, including ankyrin repeats, an SH3 domain, a PDZ domain, a long proline-rich region and an SAM domain. The PDZ domain of Shank binds to the C-terminus of guanylate kinase-associated protein (GKAP). The PDZ domain of Shankl from Rattus norvegicus and its complex with the C-terminal octapeptide of GKAP were crystallized at 294 K using polyethylene glycol 20 000 and 6000 as precipitants. Diffraction data sets from a peptide-free crystal and a complex crystal were collected to 1.8 and 3.2 Å resolution, respectively, using synchrotron radiation. The peptide-free crystal belongs to space group P2[sub 1], with unit-cell parameters a = 42.0, b - 50.3, c = 51.8 Å, β = 106.3°. The complex crystal belongs to space group P2[sub 1]2[sub 1]2[sub 1], with unit-cell parameters a = 89.4, b = 97.5, c = 108.3 Å. [ABSTRACT FROM AUTHOR]

The sixth PDZ domain from GRIPI and its complex with the octapeptide of the liprin-α1 C-terminus were crystallized at 294 K by the hanging-drop vapour-diffusion method. The native crystal belongs to space group P6122 (or P6522), with unit-cell parameters a = b = 40.3, c = 222.9 Å. The complex crystal belongs to space group R32, with unit-cell parameters a = b = 117.8, c = 102.0 Å. Native and peptide-complex diffraction data were collected to resolutions of 1.5 and 1.8 Å, respectively, using synchrotron X-rays. [ABSTRACT FROM AUTHOR]

Examines the overexpression, purification and crystallization of Helicobacter pylori quinolinic acid phosphoribosyltransferase. X-ray crystallography; Crystal space group; Unit-cell parameters.