Annika Ciragan

University of Helsinki
Supervisor: Ilkka Kilpeläinen
Funding: ISB
Date: 2009-05-14

Structural and functional studies of proteins involved in the biosynthesis of the cell wall and cell-shape determination of Gram-positive bacteria

Many bloodstream and other infections in hospitalized patients are caused by Gram-positive bacteria. In particular, Staphylococcus aureus (SA) and Enterococci spp. are important pathogens regarding nosocomial infections. These hospital-acquired infections are often caused by multidrug-resistant strains of the above mentioned bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) [1]. The mortality associated with these infections is about 20%, despite the best available antimicrobial therapy. In this study we are investigating proteins of Gram-positive bacteria that are involved in the biosynthesis of the cell wall and in cell morphogenesis.

One of these proteins is the cell-shape determining protein MreC. Depletion studies have revealed that the cell-shape determining proteins MreB, MreC and MreD are essential for viability and normal cell morphology in Gram-positive and in Gram-negative bacteria [2,3]. MreB is the bacterial homologue of the cytoskeletal protein actin [4]. Whereas the function of MreB has been extensively studied, the roles of MreC and MreD in maintaining bacterial cell shape are not well understood. MreC is a transmembrane protein in many Gram-positive bacteria such as Bacillus subtilis (BS) and SA. The major C-terminal domain of MreC is located outside the cytoplasmic membrane [2]. MreC interacts with MreB and MreD. Additionally, MreC physically associates with proteins involved in the cell wall biosynthesis, including several penicillin-binding proteins (PBPs) [2, 4, 5]. Thus, MreC probably has a critical role in the peptidoglycan biosynthesis, particularly regarding the spatial organization of PBPs [5]. Furthermore, MreC can be easily accessed by antibacterial drugs because of its localization outside the cytoplasmic membrane. Therefore, MreC is a potential target for developing new antimicrobial drugs to combat nosocomial infections.

One aim of my research is to determine the structures of the extracytoplasmic domains of BS and SA MreC using NMR spectroscopy. Furthermore, NMR will be used to study interactions of MreC with proteins involved in the peptidoglycan biosynthesis. The two organisms, BS and SA are used. BS is a widely studied model organism for Gram-positive bacteria and SA is an important pathogen. A further aim of my studies is to characterize the roles of other proteins involved in cell wall biosynthesis and cell morphogenesis of Gram-positive bacteria.