An essential serotype recognition pocket on phage P22 tailspike protein forces Salmonella enterica serovar Paratyphi A O-antigen fragments to bind as nonsolution conformers

In contrast, octasaccharides from the other serotypes bind as solution-like conformers. Two water molecules are conserved in all P22 TSP complexes with octasaccharides of different serotypes. They line the dideoxyhexose binding pocket and force the S. Paratyphi A octasaccharides to bind as nonsolution conformers. This emphasizes the role of solvent as part of carbohydrate binding sites.