4AVZ: Tailspike Protein Mutant E372q Of E. Coli Bacteriophage Hk620

Citation:
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.
PDB ID: 4AVZDownload
MMDB ID: 103282
PDB Deposition Date: 2012/5/30
Updated in MMDB: 2012/09
Experimental Method:
x-ray diffraction
Resolution: 1.82  Å
Source Organism:
Similar Structures:
Biological Unit for 4AVZ: trimeric; determined by author and by software (PISA)
Molecular Components in 4AVZ
Label Count Molecule
Proteins (3 molecules)
3
Tail Spike Protein
Molecule annotation
Chemicals (3 molecules)
1
3
* Click molecule labels to explore molecular sequence information.

Citing MMDB
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