My graduate research aims to elucidate the biochemical mechanisms of cell-wall recycling and antibiotic resistance in Gram-negative bacteria. My primary focus is on Pseudomanas aeruginosa lytic transglycosylases, a family of enzymes that cooperatively recycle the components of the cell wall, a process critical for bacterial homeostasis as well as the induction of resistance mechanisms to antibiotics. My project requires the integration of many scientific disciplines to gain a complete understanding of the mechanism of action of lytic transglycosylases. My mentor, Prof. Shahriar Mobashery, is a renowned leader in the field of bacterial resistance and antibacterial discovery and heads a team of scientists from various fields, much akin to a small pharmaceutical company. The group’s focus on cross-disciplinary research exemplifies my goal to gain a pervasive knowledge and understanding of scientific research. To engage myself in science outreach, I have presented at national conferences and served as a teacher assistant at my undergraduate institution. These opportunities have afforded me a forum for communicating science to others; an aspect of scientific training that will prove invaluable in my future career. With the support of my advisor and the strong academic education I have received from my graduate and undergraduate institutions, I am confident I will have the necessary tools to lead a successful career in science.
The Enzyme Mechanism of Family 1 Lytic Transglycosylase MltE of Escherichia coli
The integrity of the bacterial cell wall is central to viability of bacteria. Homeostasis of cell wall during bacterial growth and division requires the sophisticated integration of many pathways, which includes enzymes responsible for recycling the cell-wall components. These enzymes include lytic transglycosylases, which fragment the peptidoglycan, the major component of the cell wall. Current antibacterials that target enzymes that facilitate peptidoglycan biosynthesis include beta-lactam antibiotics. However, many bacteria have developed resistance mechanisms to beta-lactams and novel targets for new antibacterials are highly sought. Lytic transglycosylases are a diverse family of enzymes that catalyze a non-hydrolytic cyclization of the N-acetylmuramyl moiety of the peptidoglycan, resulting in the scission of the glycosidic backbone of the peptidoglycan, yielding a 1,6-anhydro-N-acetylmuramyl (1,6-anhydroMurNAc) derivative. This 1,6-anhydroMurNAc is transported from the periplasm (where cell wall exists) to the cytoplasm by the membrane protein AmpG, where it is converted to Lipid II, which is used for de novo synthesis of cell wall. This entire process sustains the integrity of the cell wall, while preserving the balance between peptidoglycan synthesis and degradation. Due to the profound importance of these enzymes in maintaining cell structure and viability, they are targets for novel antibiotics. Lytic transglycosylases demonstrate functional redundancy, but may be divided into three families diverging in both amino-acid sequence and protein structure. Family 1 lytic transglycosylases including membrane-bound lytic transglycosylases (mlt) C, D, E, F and soluble lytic transglycosylase 70 of Escherichia coli are the largest family of lytic transglycosylases and a preponderance of evidence suggests they share a mechanism of action. Herein, we present a mechanism of action of this important family of lytic tranglycosylases with data from mutant variants and from computational analyses.