5b5h
Hydrophobic ice-binding site confer hyperactivity on antifreeze protein from a snow mold fungus
Structural highlights
FunctionIBPKA_TYPIS Binds to the surface of ice crystals (Ref.1, PubMed:20030710, PubMed:27613857). Inhibits growth of the ice crystals (PubMed:20030710). Has antifreeze activity for survival under snow cover. 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:20030710, PubMed:27613857). The TH activity of this protein is 2.0 degrees Celsius at 0.11 mM (PubMed:27613857).[1] [2] [REFERENCE:1] Publication Abstract from PubMedSnow mold fungus, Typhula ishikariensis , secretes seven antifreeze protein isoforms (denoted Tis AFPs) that assist in the survival of the mold under snow cover. Here, the X-ray crystal structure of a hyperactive isoform, Tis AFP8, at 1.0 A resolution is presented. Tis AFP8 folds into a right-handed beta-helix accompanied with a long alpha-helix insertion. Tis AFP8 exhibited significantly high antifreeze activity that is comparable with other hyperactive AFPs despite its close structural and sequence similarity with the moderately active isoform Tis AFP6. A series of mutations introduced into the putative ice-binding sites (IBSs) in the beta-sheet and adjacent loop region reduced antifreeze activity. A double mutant A20T/A212S, which compose a hydrophobic patch between the beta-sheet and loop region, caused the greatest depression of antifreeze activity of 75 %, when compared with that of the wild-type protein. This shows that the loop region is involved in ice binding and hydrophobic residues play crucial functional roles. Additionally, bound waters around the beta-sheet and loop region IBSs were organized into an ice-like network and can be divided into two groups that appear to mediate separately Tis AFP and ice. The docking model of Tis AFP8 with the basal plane via its loop region IBS reveals a better shape complementarity than that of Tis AFP6. In conclusion, we present new insights into the ice-binding mechanism of Tis AFP8 by showing that a higher hydrophobicity and better shape complementarity of its IBSs, especially the loop region, may render Tis AFP8 hyperactive to ice binding. Hydrophobic Ice-Binding Sites Confer Hyperactivity of an Antifreeze Protein from a Snow Mold Fungus.,Cheng J, Hanada Y, Miura A, Tsuda S, Kondo H Biochem J. 2016 Sep 9. pii: BCJ20160543. PMID:27613857[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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