Ice Binding Proteins (IBPs) contribute to the survival of many living beings at sub-zero temperature by controlling the formation and growth of ice crystals. This work investigates the structural basis of the ice binding properties of Efc IBP, obtained from Antarctic bacteria. Efc IBP is endowed with a unique combination of thermal hysteresis (TH) and ice recrystallization inhibition (IRI) activity. The three-dimensional structure, solved at 0.84 Å resolution, shows that Efc IBP belongs to the IBP-1 fold family, and is organized in a right-handed β-solenoid with a triangular cross-section that forms three protein surfaces, named A, B and C faces. However, Efc IBP diverges from other IBP-1 fold proteins in relevant structural features including the lack of a “capping” region on top of the β-solenoid, and in the sequence and organization of the regions exposed to ice that, in Efc IBP, reveal the presence of threonine-rich ice-binding motifs. Docking experiments and site-directed mutagenesis pinpoint that Efc IBP binds ice crystals not only via its B face, as common to other IBPs, but also via ice binding sites on the C face. This article is protected by copyright. All rights reserved.
Chemistry and Pharmacology