Comparative proteomic analysis of the Haemophilus ducreyi porin-deficient mutant 35000HP::P2AB

Haemophilus ducreyi is an obligate human pathogen and the causative agent of the sexually transmitted, genital ulcerative disease chancroid. The genome of strain 35000HP contains two known porin proteins, OmpP2A and OmpP2B. Loss of OmpP2A and OmpP2B expression in the mutant 35000HP::P2AB resulted in no obvious growth defect or phenotype. Comparison of outer membrane profiles indicated increased expression of the 58.5-kDa chaperone, GroEL, in the porin-deficient mutant. A proteomics-based comparison resulted in the identification of 231 proteins present in membrane-associated protein samples, of which a subset of 56 proteins was differentially expressed at a level of 1.5-fold or greater in the porin-deficient strain 35000HP::P2AB relative to that in 35000HP. Twenty of the differentially expressed proteins were selected for real-time PCR, resulting in the validation of 90% of the selected subgroup. Proteins identified in these studies suggested a decreased membrane stability phenotype, which was verified by disk diffusion assay. Loss of OmpP2A and OmpP2B resulted in global protein expression changes which appear to compensate for the absence of porin expression in 35000HP::P2AB.