title: Low resolution solution structure of the Apo form of Escherichia coli haemoglobin protease Hbp.
abstract: We have studied the solution properties of the apo form of the haemoglobin protease or "haemoglobinase", Hbp, a principal component of an important iron acquisition system in pathogenic Escherichia coli. Experimental determination of secondary structure content from circular dichroism (CD) spectroscopy, obtained using synchrotron light, showed that the protein contains predominately beta-sheets in agreement with secondary structure prediction from the primary sequence. Next, the size and shape of the protein were probed using analytical ultracentrifugation (AUC) and small angle X-ray scattering (SAXS). These showed that Hbp is a monomer, with an extended conformation. Using ab initio reconstruction methods we have produced a model of Hbp, which shows that the protein adopts an extended crescent-shaped conformation. Analysis of the resulting model gives hydrodynamic parameters in good agreement with those observed experimentally. Thus we are able to construct a hydrodynamically rigorous model of apo-Hbp in solution, not only giving a greater level of confidence to the results of the SAXS reconstruction methods, but providing the first three-dimensional view of this intriguing molecule.
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, YO10 5DD, UK. david.scott@bristol.ac.uk
authors.forename: David J
authors.initials: DJ
authors.lastname: Scott
authors.forename: J Günter
authors.initials: JG
authors.lastname: Grossmann
authors.forename: Jeremy R H
authors.initials: JR
authors.lastname: Tame
authors.forename: Olwyn
authors.initials: O
authors.lastname: Byron
authors.forename: Keith S
authors.initials: KS
authors.lastname: Wilson
authors.forename: Ben R
authors.initials: BR
authors.lastname: Otto
mesh_terms: D001051:Apoenzymes / Q000737:chemistry*; D002942:Circular Dichroism; D010450:Endopeptidases / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012984:Software; D012996:Solutions; D017356:Synchrotrons; D014461:Ultracentrifugation; D014961:X-Ray Diffraction
chemical_list: D001051:Apoenzymes; D012996:Solutions; D010450:Endopeptidases; C114676:hemoglobin protease Hbp