PTS_IIB_fructose: subunit IIB of enzyme II (EII) of the fructose-specific phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). In this system, EII (also referred to as FruAB) is a fructose-specific permease made up of two proteins (FruA and FruB) each containing 3 domains. The FruA protein contains two tandem nonidentical IIB domains and a C-terminal IIC transmembrane domain. Both IIB domains of FruA are included in this alignment. The FruB protein (also referred to as diphosphoryl transfer protein) contains a IIA domain, a domain of unknown function, and an Hpr-like domain called FPr (fructose-inducible HPr). This familiy also includes the IIB domains of several fructose-like PTS permeases including the Frv permease encoded by the frvABXR operon, the Frw permease encoded by the frwACBD operon, the Frx permease encoded by the hrsA gene, and the Fry permease encoded by the fryABC (ypdDGH) operon. FruAB takes up exogenous fructose, releasing the 1-phosphate ester in to the cytoplasm in preparation for metabolism primarily via glycolysis. The IIB domain fold includes a central four-stranded parallel open twisted beta-sheet flanked by alpha-helices on both sides. The seven major PTS systems with this IIB fold include fructose, chitobiose/lichenan, ascorbate, lactose, galactitol, mannitol, and a sensory system with similarity to the bacterial bgl system.
Comment:most of the active site residues are contained within a P-loop which forms part of a binding pocket for the phosphoryl group
Comment:for the E coli chitobiose transporter IIB subunit,(not included in this IIB subgroup) in addition to the P-loop residues, two conserved residues are likely to be important in catalysis: a tyrosine whose side-chain points towards the phosphorylation site and a Gln residue whose side-chain lies close to the sulfur atom of the catalytic cysteine.