4nu3
Crystal structure of mFfIBP, a capping head region swapped mutant of ice-binding protein
Structural highlights
FunctionIBP_FLAFP Has antifreeze activity for survival in a subzero environment. Binds to the surface of ice crystals and inhibits their growth. Has high thermal hysteresis (TH) activity, which is the ability to lower the freezing point of an aqueous solution below its melting point, and thus the freezing of the cell fluid can be prevented protecting the organism from ice damage (PubMed:22750870, PubMed:24699650, PubMed:27737617). The TH activity of this protein is 2.2 degrees Celsius at 5 uM and 2.5 degrees Celsius at 50 uM (PubMed:24699650).[1] [2] [3] Publication Abstract from PubMedIce-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 A 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 alpha2 and alpha4 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. Structure-based characterization and antifreeze properties of a hyperactive ice-binding protein from the Antarctic bacterium Flavobacterium frigoris PS1.,Do H, Kim SJ, Kim HJ, Lee JH Acta Crystallogr D Biol Crystallogr. 2014 Apr 1;70(Pt 4):1061-73. doi:, 10.1107/S1399004714000996. Epub 2014 Mar 19. PMID:24699650[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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