Jel44 monoclonal Fab fragment specific for HPr of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli and the complex of Jel44 Fab fragment with HPr: preparation, crystallization and preliminary crystallographic analysis

Jel44 is a mouse monoclonal antibody specific for the histidine-containing phosphocarrier protein (HPr), a component of a sugar-transport system in Escherichia coli. Because Jel44 binding to HPr is dependent upon ionic strength and the enthalpic and entropic contributions do not vary over the temperature range 277–310 K, the complex is of great interest. A single crystal of the Jel44 Fab fragment was obtained and diffracted X-rays to a maximum resolution of 4.6 Å on an in-house X-ray source. The crystal belongs to space group P2₁, with unit-cell parameters a = 68.6, b = 67.7, c = 105.5 Å, β = 96°. Although crystals of the complex of Jel44 Fab fragment with HPr could not be fully characterized owing to suspected crystal twinning, it was encouraging that they diffracted X-rays to 2.5 Å on an in-house X-ray source. It is thus foreseen that improvement of crystal quality will allow the complete solution of this novel structure.