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The metalloprotease PrtV from Vibrio cholerae serves an important function for the bacteria's ability to invade the mammalian host cell. The protein belongs to the family of M6 proteases, with a characteristic zinc ion in the catalytic active site. PrtV constitutes a 918 amino acids (102kDa) multidomain pre-pro-protein that so far has only been expressed in V. cholerae. Structural studies require high amounts of soluble protein with high purity. Previous attempts for recombinant expression have been hampered by low expression and solubility of protein fragments. Here, we describe results from parallel cloning experiments in Escherichia coli where fusion tagged constructs of PrtV fragments were designed, and protein products tested for expression and solubility. Of more than 100 designed constructs, three produced protein products that expressed well. These include the N-terminal domain (residues 23-103), the PKD1 domain (residues 755-839), and a 25kDa fragment (residues 581-839). The soluble fusion proteins were captured with Ni(2+) affinity chromatography, and subsequently cleaved with tobacco etch virus protease. Purification protocols yielded ∼10-15mg of pure protein from 1L of culture. Proper folding of the shorter domains was confirmed by heteronuclear NMR spectra recorded on (15)N-labeled samples. A modified protocol for the native purification of the secreted 81kDa pro-protein of PrtV is provided. Proteolytic activity measurements suggest that the 37kDa catalytic metalloprotease domain alone is sufficient for activity.

Vibrio cholerae, the causative agent of cholera, releases several virulence factors including secreted proteases when it infects its host. These factors attack host cell proteins and break down tissue barriers and cellular matrix components such as collagen, laminin, fibronectin, keratin, elastin, and they induce necrotic tissue damage. The secreted protease PrtV constitutes one virulence factors of V. cholerae. It is a metalloprotease belonging to the M6 peptidase family. The protein is expressed as an inactive, multidomain, 102 kDa pre-pro-protein that undergoes several N- and C-terminal modifications after which it is secreted as an intermediate variant of 81 kDa. After secretion from the bacteria, additional proteolytic steps occur to produce the 55 kDa active M6 metalloprotease. The domain arrangement of PrtV is likely to play an important role in these maturation steps, which are known to be regulated by calcium. However, the molecular mechanism by which calcium controls proteolysis is unknown. In this study, we report the atomic resolution crystal structure of the PKD1 domain from V. cholera PrtV (residues 755–838) determined at 1.1 Å. The structure reveals a previously uncharacterized Ca²⁺-binding site located near linker regions between domains. Conformational changes in the Ca²⁺-free and Ca²⁺-bound forms suggest that Ca²⁺-binding at the PKD1 domain controls domain linker flexibility, and plays an important structural role, providing stability to the PrtV protein.

The transcription factor FocB belongs to a family of regulators encoded by several different fimbriae gene clusters in uropathogenic Escherichia coli. Recent findings suggest that FocB-family proteins may form different protein-protein complexes and that they may exert both positive and negative effects on the transcription of fimbriae genes. However, little is known about the actual role and mode of action when these proteins interact with the fimbriae operons. The 109-amino-acid FocB transcription factor from the foc gene cluster in E. coli strain J96 has been cloned, expressed and purified. The His₆-tagged fusion protein was captured by Ni²⁺-affinity chromatography, cleaved with tobacco etch virus protease and purified by gel filtration. The purified protein is oligomeric, most likely in the form of dimers. NMR analysis guided the crystallization attempts by showing that probable conformational exchange or oligomerization is reduced at temperatures above 293 K and that removal of the highly flexible His₆ tag is advantageous. The protein was crystallized using the hanging-drop vapour-diffusion method at 295 K. A native data set to 2.0 Å resolution was collected at 100 K using synchrotron radiation.

Viscotoxins are small cationic proteins found in European mistletoe Viscum album. They are highly toxic towards phytopathogenic fungi and cancer cells. Heterologous expression of viscotoxins would broaden the spectrum of methods to be applied for better understanding of their structure and function and satisfy possible biopharmaceutical needs. Here, we evaluated 13 different proteins as a fusion partners for expression in Escherichia coli cells: His6 tag and His6-tagged versions of GB1, ZZ tag, Z tag, maltose binding protein, NusA, glutathione S-transferase, thioredoxin, green fluorescent protein, as well as periplasmic and cytosolic versions of DsbC and DsbA. The fusion to thioredoxin gave the highest yield of soluble viscotoxin. The His6-tagged fusion protein was captured with Ni(2+) affinity chromatography, subsequently cleaved with tobacco etch virus protease. Selective precipitation by acidification of the cleavage mixture was followed by cation exchange chromatography. This protocol yielded 5.2 mg of visctoxin A3 from 11 of culture medium corresponding to a recovery rate of 68%. Mass spectrometry showed a high purity of the sample and the presence of three disulfide bridges in the recombinant viscotoxin. Proper folding of the protein was confirmed by heteronuclear NMR spectra recorded on a uniformly 15N-labeled sample. Recombinant viscotoxins prepared using this protocol are toxic to HeLa cells and preserve the activity differences between isoforms B and A3 found in native proteins.

Monooxygenases are frequently involved in the pathways that mediate the pivotal role of microorganisms in recycling carbon from the environment. A structural study of a monooxygenase from Pseudomonas aeruginosa that was identified as a phenylalanine hydroxylase has been initiated. The single-domain monomeric protein harbours a non-haem iron at the active site. The sequence identity to the catalytic domains of tyrosine and tryptophan hydroxylases suggests that the enzyme is not restricted to the substrate phenylalanine alone. Here, the cloning, purification and crystallization of native and SeMet-labelled P. aeruginosa phenylalanine hydroxylase are reported. Crystals grew in space group P6(1), with unit-cell parameters a = b = 210.5, c = 100.7 A, and diffracted to a d spacing of 2.0 A. Crystals of SeMet-labelled protein were used to collect a three-wavelength multiple anomalous dispersion (MAD) data set around the Se K edge.

Alpha-actinin forms antiparallel homodimers that cross-link actin filaments from adjacent sarcomeres within the Z-discs of striated muscle. The N-terminal actin-binding domain (ABD) is composed of two calponin homology (CH) domains followed by four spectrin-like repeats and a calmodulin-like EF-hand domain at the C-terminus. The ABD of human alpha-actinin crystallizes in space group P2(1), with unit-cell parameters a = 101.9, b = 38.4, c = 154.9 A, beta = 109.2 degrees. A complete native data set from a native crystal was collected extending to 2.0 A resolution and a single-wavelength anomalous dispersion (SAD) data set to 2.9 A resolution was collected from a selenomethionine-labelled microcrystal using the microfocusing beamline ID-13 at the ESRF. Analysis of the anomalous contribution shows a rapid decrease in the sigma(normal)/sigma(anomal) ratio owing to radiation damage.