Structures and ice-binding faces of the alanine-rich type I antifreeze proteins.
Antifreeze proteins (AFPs) protect cold-blooded organisms from the damage caused by freezing through their ability to inhibit ice growth. The type I AFP family, found in several fish species, contains proteins that have a high alanine content (>60% of the sequence) and structures that are almost all alpha-helical. We examine the structure of the type I AFP isoforms HPLC6 from winter flounder, shorthorn sculpin 3, and the winter flounder hyperactive type I AFP. The HPLC6 isoform structure consists of a single alpha-helix that is 37 residues long, whereas the shorthorn sculpin 3 isoform consists of two helical regions separated by a kink. The high-resolution structure of the hyperactive type I AFP has yet to be determined, but circular dichroism data and analytical ultracentrifugation suggest that the 195 residue protein is a side-by-side dimer of two alpha-helices. The alanine-rich ice-binding faces of HPLC6 and hyperactive type I AFP are discussed, and we propose that the ice-binding face of the shorthorn sculpin 3 AFP contains Ala14, Ala19, and Ala25. We also propose that the denaturation of hyperactive type I AFP at room temperature is explained by the stabilization of the dimerization interface through hydrogen bonds.
Patel
Shruti N
SN
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
Graether
Steffen P
SP
D000409:Alanine / Q000032:analysis* / Q000737:chemistry*; D021322:Antifreeze Proteins, Type I / Q000737:chemistry*; D001665:Binding Sites; D007053:Ice; D011487:Protein Conformation
D021322:Antifreeze Proteins, Type I; D007053:Ice; D000409:Alanine