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 A on an in-house X-ray source. The crystal belongs to space group P2(1), with unit-cell parameters a = 68.6, b = 67.7, c = 105.5 A, beta = 96 degrees. 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 A 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.