Superlong, ice-binding protein structure solved

Abstract

Researchers have obtained the first structure of a 600-nm-long, ice-binding protein. Few proteins are this long; one exception is the muscle protein titin, which is more than 1 µm long. Most folded proteins are 2 to 15 nm long. The ice-binding protein, called Marinomonas primoryensis ice-binding protein (MpIBP), is expressed on the surface of an Antarctic bacterium, which uses the protein to latch onto the underside of ice sheets. In this near-surface, sunlit location, the bacteria can cohabit with diatoms, which photosynthesize oxygen that the bacteria need. MpIBP’s single protein chain has five regions: RI, RII, RIII, RIV, and RV. Peter L. Davies of Queen’s University in Ontario, Ilja K. Voets of Eindhoven University of Technology, and coworkers earlier obtained X-ray crystal structures of RII and RIV. They have now used X-ray crystallography, nuclear magnetic resonance, and small-angle X-ray scattering to analyze RI, RIII, and RV, enabling them to assemble