Chromosomal His-tagging: An alternative approach to membrane protein purification

Peptide translocation across MOMP, the major outer membrane channel from Campylobacter jejuni

Here we report on translocation of short poly-arginines across the MOMP porin, the major outer membrane protein in the cell wall of Campylobacter jejuni. MOMP was purified to homogeneity from a pathogenic strain of C. jejuni. Its reconstitution in lipid membranes and measuring the ion-current revealed two main distinct populations of protein channels which we interpreted as mono and trimers. Addition of poly-arginines causes concentration and voltage dependent ion-current fluctuations. Increasing the transmembrane potential decreases the residence time of the peptide inside the channel indicating successful translocation. We conclude that poly-arginines can cross the outer membrane of Campylobacter through the MOMP channel.

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Translocation of short poly-arginines across the MOMP channel has been determined.

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Penta-arginine and Hepta-arginine translocate across the MOMP channel.

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Voltage dependent kinetics to distinguish binding from translocation.

Validation of a Burkholderia pseudomallei hypothetical protein and determination of its translational start codon using chromosomal integration of His-Tag coding sequence

In this post genomic era, there are a great number of in silico annotated hypothetical genes. However, experimental validation of the functionality of these genes remains tentative. Two of the major challenges faced by researcher are whether these hypothetical genes are protein-coding genes and whether their corresponding predicted translational start codons are correct. In this report, we demonstrate a convenient procedure to validate the presence of a hypothetical gene product of BPSS1356 from Burkholderia pseudomallei as well as its start codon. It was done by integration of a His-Tag coding sequence into C-terminal end of BPSS1356 gene via homologous recombination. We then purified the native protein using affinity chromatography. The genuine start codon of BPSS1356 was then determined by protein N-terminal sequencing.

Expression patterns and role of the CadF protein in Campylobacter jejuni and Campylobacter coli

Binding of Campylobacter jejuni and Campylobacter coli to host fibronectin is mediated by the 37 kDa outer membrane protein CadF. Immunoblot analysis of 58 C. jejuni and C. coli isolates of human and animal origin showed that CadF is expressed in every strain. In most C. jejuni isolates, a 37 kDa band (p37) and a less-prominent 32 kDa band (p32) reacted with the antibodies. In C. coli isolates, CadF was consistently larger with sizes of 39 kDa (p39) and 34 kDa (p34), respectively. PCR analysis and sequencing revealed the presence of a 39-bp insertion sequence in the cadF gene of C. coli strains, explaining the increased molecular size. Infection assays revealed that C. jejuni bound and invaded INT-407 epithelial cells much more efficiently than C. coli and that this difference was considerably reduced in isogenic cadF mutants. These results demonstrate that CadF is an important pathogenicity factor. The difference between CadF of C. jejuni and C. coli may potentially be exploited to discriminate these species in food and clinical specimens.