Pathogenic bacteria have developed a broad range of molecular strategies to invade and colonize their hosts by highly unique and specialized mechanisms that enable them to cross barriers and overcome multiple defense systems. The knowledge, at the atomic level, of structures and interactions is essential to understand the enantio- and stereospecific requirements necessary to decipher the mechanisms involved in the proliferation and pathogenic spread. This cluster of information is the key to combating pathogens and, in recent years, our research has focused on the inhibition of diseases by means of (I) the arginine repressor protein (ArgR) and (II) Phospholipase D (PLD) from Corynebacterium pseudotuberculosis and (III) of the exfoliative toxin D (ETD) from Staphylococcus aureus, which play a central roles in the spread of the pathogens in the host. (I) Arginine repressor (ArgR), coordinates the expression of genes involved in arginine biosynthesis. After attaining a specific concentration of arginine in the cytoplasm, arginine interacts with the ArgR and the complex formed (ArgR / Arg) is coupled to the DNA promoter, interrupting synthesis. We determined the structure of the wild type and mutant ArgR, and analyzed the binding pocket that determines its specificity and we have also screened for ligands that induces hexamerization and regulates the allosteric effect of this enzyme, thereby inhibiting the arginine synthesis pathway and consequently stopping proliferation of the pathogen. (II) Phospholipase D (PLD) which is in reality a sphingomyelinase, is the key factor in determining virulence of the pathogen and one of the main candidates for vaccine development. PLD has a glycoprotein exotoxin action and is capable of hydrolyzing sphingomyelin, favoring infection and dissemination of the pathogen from the primary infection site to the lymph nodes. (III) Virulent strains of Staphylococcus aureus secrete exfoliative toxins (ETs) that cause loss of cell adhesion in the epidermis of several hosts. S. aureus ETs are enzymes with high specificity for their substrate desmoglein 1 (Dsg1) and their mechanisms of action are complex with many peculiarities that distinguish them from other serine proteinases. Dsg1 is a cell adhesion protein in the epidermis and is selectively cleaved by the ETs. Residues between positions 271 to 277 of human and murine Dsg1 are crucial for the cleavage of the substrate Glu381-Gly382 peptide bond. Peptides designed based on Dsg1 will be used to inhibit the coupling of ETD with its substrate and consequently prevent the exfoliation process.
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