Abstract
The Peptidoglycan (PG) is one of the main components of the bacterial cell wall, being responsible to maintain the form and integrity of the cell. As an essential component for bacterial survival and found only in prokaryotic organisms, the PG biosynthesis has been widely explored for the development of antibiotics, even in the face of the global crisis caused by the antibiotic resistance increase. PG biosynthesis is a dynamic and highly complex process mediated by a group of proteins localized at different parts of the cell. Mur ligases (MurC, MurD, MurE, and MurF) are cytoplasmatic enzymes that, together with MurG (membrane-associated protein) and MraY (membrane protein), are responsible for the synthesis of the PG precursors. These proteins have been extensively studied and characterized individually, and, even though inhibitors have been found for them in vitro, they do not show clear antibacterial intracellular activity. A hypothesis would be that the Mur ligases form a mega-complex which could facilitate the formation of the PG subunit and, somehow, it could mask the active sites of the proteins. Different research groups demonstrated that the cytoplasmatic proteins of the PG biosynthesis can identify each other, and, recently, our research group identified that the Mur ligases from Streptococcus pneumoniae can interact strongly as binary complexes. However, until now, the complex between these proteins have not been reported. In our preliminary essays, we were able to express and purify at least three Mur ligases together with MurG, showing promising results towards the characterization of a Mur enzyme complex, essential for PG biosynthesis, using an innovative technique: the expression with the operon system naturally found in microorganisms. Biochemical and biophysical techniques will be used to analyze the interactions of the proteins in the complex. Furthermore, crystallization essays and/or electron microscopy will be used to characterize this complex structurally. The results of this project will provide more detailed information on the PG biosynthesis, and the interactions between these proteins, assisting the pharmaceutical industry in the development of more efficient drugs. (AU)
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