Identification and characterization of smallest pore-forming protein in the cell wall of pathogenic Corynebacterium urealyticum DSM 7109

Narges Abdali,Karunakar R Pothula,Samaneh Mafakheri,Farhan Younas,Roland Benz,Andreas Tauch,Ulrich Kleinekathöfer

doi:10.1186/s12858-018-0093-9

Abstract

BackgroundCorynebacterium urealyticum, a pathogenic, multidrug resistant member of the mycolata, is known as causative agent of urinary tract infections although it is a bacterium of the skin flora. This pathogenic bacterium shares with the mycolata the property of having an unusual cell envelope composition and architecture, typical for the genus Corynebacterium. The cell wall of members of the mycolata contains channel-forming proteins for the uptake of solutes.ResultsIn this study, we provide novel information on the identification and characterization of a pore-forming protein in the cell wall of C. urealyticum DSM 7109. Detergent extracts of whole C. urealyticum cultures formed in lipid bilayer membranes slightly cation-selective pores with a single-channel conductance of 1.75 nS in 1 M KCl. Experiments with different salts and non-electrolytes suggested that the cell wall pore of C. urealyticum is wide and water-filled and has a diameter of about 1.8 nm. Molecular modelling and dynamics has been performed to obtain a model of the pore. For the search of the gene coding for the cell wall pore of C. urealyticum we looked in the known genome of C. urealyticum for a similar chromosomal localization of the porin gene to known porH and porA genes of other Corynebacterium strains. Three genes are located between the genes coding for GroEL2 and polyphosphate kinase (PKK2). Two of the genes (cur_1714 and cur_1715) were expressed in different constructs in C. glutamicum ΔporAΔporH and in porin-deficient BL21 DE3 Omp8 E. coli strains. The results suggested that the gene cur_1714 codes alone for the cell wall channel. The cell wall porin of C. urealyticum termed PorACur was purified to homogeneity using different biochemical methods and had an apparent molecular mass of about 4 kDa on tricine-containing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).ConclusionsBiophysical characterization of the purified protein (PorACur) suggested indeed that cur_1714 is the gene coding for the pore-forming protein in C. urealyticum because the protein formed in lipid bilayer experiments the same pores as the detergent extract of whole cells. The study is the first report of a cell wall channel in the pathogenic C. urealyticum.

Highlights

Corynebacterium urealyticum, a pathogenic, multidrug resistant member of the mycolata, is known as causative agent of urinary tract infections it is a bacterium of the skin flora
Cell wall proteins from C. urealyticum effect the conductance of lipid bilayer membranes Cells of a C. urealyticum culture grown overnight were extracted with 1% LDAO
Control experiments with LDAO alone at the same concentration as in the experiments with extracts demonstrated that the membrane activity was caused by the presence of the extracts and not by the detergent. This result suggested that the channel-forming activity was an intrinsic property of the detergent extracts of whole C. urealyticum cells

Summary

Introduction

Corynebacterium urealyticum, a pathogenic, multidrug resistant member of the mycolata, is known as causative agent of urinary tract infections it is a bacterium of the skin flora. This pathogenic bacterium shares with the mycolata the property of having an unusual cell envelope composition and architecture, typical for the genus Corynebacterium. Selective transport of molecules through the cell wall is crucial to the life-or-death of bacterial cells [1, 2] They continuously need to exchange small molecules, nutrients and proteins with the exterior environment, while they need to keep toxic substances out [3,4,5]. Non-pathogenic corynebacteria are used for the production of amino acids such as L-glutamate and L-lysine at industrial scale [8]

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