4xqf

<table><tr><td colspan='2'>[[4xqf]] is a 1 chain structure with sequence from [http://en.wikipedia.org/wiki/Bphk6 Bphk6]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4XQF OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=4XQF FirstGlance]. <br>

</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat"><scene name='pdbligand=FMT:FORMIC+ACID'>FMT</scene>, <scene name='pdbligand=NA:SODIUM+ION'>NA</scene>, <scene name='pdbligand=TRS:2-AMINO-2-HYDROXYMETHYL-PROPANE-1,3-DIOL'>TRS</scene></td></tr>

<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=4xqf FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4xqf OCA], [http://pdbe.org/4xqf PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=4xqf RCSB], [http://www.ebi.ac.uk/pdbsum/4xqf PDBsum], [http://prosat.h-its.org/prosat/prosatexe?pdbcode=4xqf ProSAT]</span></td></tr>

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== Publication Abstract from PubMed ==

Bacteriophage HK620 recognizes and cleaves the Oantigen polysaccharide of E. 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: Firstly, 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. Secondly, a region where 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.

 

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== References ==

[[Category: Bphk6]]

[[Category: Barbirz, S]]

[[Category: Broeker, N K]]

[[Category: Gohlke, U]]

[[Category: Heinemann, U]]

[[Category: Seckler, R]]

[[Category: Viral protein]]