PMID:22923442

Citation	Broeker, NK, Gohlke, U, Müller, JJ, Uetrecht, C, Heinemann, U, Seckler, R and Barbirz, S (2013) Single amino acid exchange in bacteriophage HK620 tailspike protein results in thousand-fold increase of its oligosaccharide affinity. Glycobiology 23:59-68
Abstract	Bacteriophage HK620 recognizes and cleaves the O-antigen polysaccharide of Escherichia coli serogroup O18A1 with its tailspike protein (TSP). HK620TSP binds hexasaccharide fragments with low affinity, but single amino acid exchanges generated a set of high-affinity mutants with submicromolar dissociation constants. Isothermal titration calorimetry showed that only small amounts of heat were released upon complex formation via a large number of direct and solvent-mediated hydrogen bonds between carbohydrate and protein. At room temperature, association was both enthalpy- and entropy-driven emphasizing major solvent rearrangements upon complex formation. Crystal structure analysis showed identical protein and sugar conformers in the TSP complexes regardless of their hexasaccharide affinity. Only in one case, a TSP mutant bound a different hexasaccharide conformer. The extended sugar binding site could be dissected in two regions: first, a hydrophobic pocket at the reducing end with minor affinity contributions. Access to this site could be blocked by a single aspartate to asparagine exchange without major loss in hexasaccharide affinity. Second, a region where the specific exchange of glutamate for glutamine created a site for an additional water molecule. Side-chain rearrangements upon sugar binding led to desolvation and additional hydrogen bonding which define this region of the binding site as the high-affinity scaffold.
Links	PubMed Online version:10.1093/glycob/cws126
Keywords	Amino Acids; Asparagine/genetics; Asparagine/metabolism; Aspartic Acid/genetics; Aspartic Acid/metabolism; Binding Sites; Catalytic Domain; Coliphages/metabolism; Crystallography, X-Ray; Hydrogen Bonding; Models, Molecular; O Antigens/chemistry; O Antigens/metabolism; Oligosaccharides/chemistry; Oligosaccharides/metabolism; Protein Conformation; Surface Properties; Thermodynamics; Viral Tail Proteins/chemistry; Viral Tail Proteins/genetics; Viral Tail Proteins/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
9CAUD:A0A024B0X2		GO:0098020: virus tail, minor subunit	ECO:0000314:		C		found GO id and determined it was a functional protein from article	complete CACAO 11456
9CAUD:A0A024B0X2		GO:0098018: viral capsid, minor subunit	ECO:0000314:		C		Figure 3 and Tables 1 though 3 give us information that the gene from the mutant phage was indeed interacting with the E. coli virus host.	complete CACAO 12020

References

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