The Ensemble of Conformations of Antifreeze Glycoproteins (AFGP8): A Study Using Nuclear Magnetic Resonance Spectroscopy.

• Published in: Biomolecules
• Main Authors: Her, Cheenou, Yeh, Yin, Krishnan, Viswanathan V
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2019
• Subjects: Water; Dimethyl Sulfoxide; Antifreeze Proteins; Magnetic Resonance Spectroscopy; Amino Acid Motifs; Protein Conformation; Models; Molecular; AFGP; NMR; ensemble of structures; Bioengineering; Biochemistry and Cell Biology; Antarc*; Antarctic; Arctic cod
• Online Access: https://escholarship.org/uc/item/2pc092q9; https://escholarship.org/content/qt2pc092q9/qt2pc092q9.pdf; https://doi.org/10.3390/biom9060235

The primary sequence of antifreeze glycoproteins (AFGPs) is highly degenerate, consisting of multiple repeats of the same tripeptide, Ala-Ala-Thr*, in which Thr* is a glycosylated threonine with the disaccharide beta-d-galactosyl-(1,3)-alpha-N-acetyl-d-galactosamine. AFGPs seem to function as intrinsically disordered proteins, presenting challenges in determining their native structure. In this work, a different approach was used to elucidate the three-dimensional structure of AFGP8 from the Arctic cod Boreogadussaida and the Antarctic notothenioid Trematomusborchgrevinki. Dimethyl sulfoxide (DMSO), a non-native solvent, was used to make AFGP8 less dynamic in solution. Interestingly, DMSO induced a non-native structure, which could be determined via nuclear magnetic resonance (NMR) spectroscopy. The overall three-dimensional structures of the two AFGP8s from two different natural sources were different from a random coil ensemble, but their "compactness" was very similar, as deduced from NMR measurements. In addition to their similar compactness, the conserved motifs, Ala-Thr*-Pro-Ala and Ala-Thr*-Ala-Ala, present in both AFGP8s, seemed to have very similar three-dimensional structures, leading to a refined definition of local structural motifs. These local structural motifs allowed AFGPs to be considered functioning as effectors, making a transition from disordered to ordered upon binding to the ice surface. In addition, AFGPs could act as dynamic linkers, whereby a short segment folds into a structural motif, while the rest of the AFGPs could still be disordered, thus simultaneously interacting with bulk water molecules and the ice surface, preventing ice crystal growth.