Alteration in abundance of specific membrane proteins of Aggregatibacter actinomycetemcomitans is attributed to deletion of the inner membrane protein MorC

Abstract

Aggregatibacter actinomycetemcomitans is an important pathogen in the etiology of human periodontal and systemic diseases. Inactivation of the gene coding for the inner membrane protein, morphogenesis protein C (MorC), results is pleotropic effects pertaining to the membrane structure and function of this bacterium. The role of this protein in membrane biogenesis is unknown. To begin to understand the role of this conserved protein, stable isotope dimethyl labeling in conjunction with mass spectrometry was used to quantitatively analyze differences in the membrane proteomes of the isogenic mutant and wild-type strain. A total of 613 proteins were quantified and 601 of these proteins were found to be equal in abundance between the two strains. The remaining 12 proteins were found in lesser (10) or greater (2) abundance in the membrane preparation of the mutant strain compared with the wild-type strain. The 12 proteins were ascribed functions associated with protein quality control systems, oxidative stress responses, and protein secretion. The potential relationship between these proteins and the phenotypes of the morC mutant strain is discussed.

Inner-membrane protein MorC is involved in fimbriae production and biofilm formation in Aggregatibacter actinomycetemcomitans

“…Disruption of this secretion system results in a reduction of the virulence potential of a number of bacteria including Klebsiella pneumoniae, Proteus mirabilis, Citrobacter rodentium and Salmonella enterica (Burall et al, 2004;Selkrig et al, 2012;Struve et al, 2003). The TamA/B complex is required for the efficient secretion of specific autotransporter proteins to the outer membrane in Enterobacteriaceae (Selkrig et al, 2012), in contrast to what is observed in morC mutants of A. actinomycetemcomitans, which express WT levels of known autotransporters (Smith et al, 2015a), which can easily be visualized by electron microscopy (Azari et al, 2013;Gallant et al, 2008).…”

“…A recent quantitative membrane proteomic study revealed a consistent decrease in the abundance of the proteins of the fimbrial secretion apparatus in the morC mutant strain when compared with the parent strain (Smith et al, 2015a). To fully comprehend the significance of these results, it was necessary first to determine the molecular basis of the defect that caused the afimbriation of the parent strain and secondly to complement and restore fimbrial production.…”

“…Loss of morphogenesis protein C (MorC) in the membrane results in conversion of the membrane morphology from rugose to flat, decreasing the surface area of the outer membrane by up to 20 % (Azari et al, 2013;Gallant et al, 2008). In addition to this dramatic morphological change, the absence of MorC results in multiple membrane-related effects including a 30 % decrease in cell size, a 70 % increase in autoaggregation, an 86 % impaired secretion of leukotoxin and a fourfold increase in sensitivity to membranedestabilizing agents (Smith et al, 2015a).…”

“…In the aforementioned proteomics study (Smith et al, 2015a), the reduction in fimbriae-associated proteins in the morC mutant strain indicated a link between MorC and fimbriae formation. In the present study, we first identified the defect for fimbriae production in a laboratory, afimbriated strain of A. actinomycetemcomitans and complemented fimbriation in this strain by introducing a plasmid expressing the fimbrial structural subunit (Flp1) and the prepilin peptidase (TadV).…”

“…These effects include a reduction in the abundance of fimbriae-associated proteins (Smith et al, 2015a). Fimbriae of A. actinomycetemcomitans are associated with 'non-specific' adherence of the organism to both biotic and abiotic surfaces and favour the formation of a tenacious biofilm (Fine et al, 1999).…”