Structural determinants of necrotic and epidermolytic activity of exfoliative protein C (ExhC) of Staphylococcus sciuri

Abstract

Staphylococcus sciuri is a commensal and pathogenic bacterium of significant clinical and veterinary relevance. Recently, a strain of S. sciuri has been described as the etiologic agent of Exudative Epidermitis in pigs in China and the main virulence factor involved in this clinical manifestation was the exfoliative protein C (ExhC). ExhC of S. sciuri, in addition to causing epidermal exfoliation in pigs and newborn rats, it was able to induce cell necrosis in vitro, specifically in the cell line of renal fibroblasts of newborn hamsters (BHK-21) a property hitherto fore unobserved in Exfoliative Toxins (ETs). The production of ExhC recombinant fragments allowed us to conclude that the domain containing residues 79-128 is responsible for the observed necrotic activity. The amino acids of the necrotic domain were aligned with the corresponding regions of the other ETs which indicated the presence of conserved amino acid residues or with similar biochemical properties in most of the ETs except in ExhC of S. sciuri. This in silico evaluation formed the basis for the design and expression of ExhC protein with mutation in four amino acid residues and lacking necrotic activity in the in vitro tests with the cell line BHK-21. Due to the experimental success of the preliminary results, the main objective of this study was to verify, specifically, which of these mutated amino acids in the aforementioned domain are essential for necrotic activity of this enzyme and to determine the structural details and specific interactions of the necrotic domain to better understand the specificities of its mechanism of action and to identify possible inhibitors for this activity. These experiments will also be carried out with a chimeric ETD exfoliative protein, with the substitution of the corresponding region with the 79-128 amino acid residues of the ExhC protein, to evaluate the effects of this substitution. In addition, the mechanism of exfoliative epidermal action of the ExhC of S. sciuri will also be investigated by analyzing specific interactions between this enzyme and its substrates: swine and murine desmoglein-1. (AU)