MRSA Treatment and Molecular Geometry/ Bonding Pharmaceutical Chemistry TIP By: James Gorman Dr. Philip Deshong University of Maryland

Warm-up Activity Comment on the following: “Though there are several types of staph infections, the one causing concern among health professions is methicillin- resistant staphylococcus aureus, or MRSA, a bacterium that is resistant to certain types of antibiotics. Several cases of MRSA have been confirmed in Massachusetts this fall, including schools in Winchester and Wrentham.” (Lefferts, Jennifer F. 2007)

Overview  Prevalence of Staphylococcus aureus  Cell Wall - Importance and Structure  Cell Wall - Construction  Cell Wall – Antibiotic target  Overview of methicillin resistance  Vancomycin  Vancomycin resistance

S. aureus Prevalence % Nasal Colonization of Population  Permanently - 20%  Transient - 60%  Never- 20% (Peacock et al. 2001) EM image of S. aureus (Paustian 2006)

Cell Wall – Importance & Structure  Mechanically supports the more flimsy cell membrane.  nm thick  Composed of  Peptidoglycans  Teichoic acids  Surface proteins (Todar 2005)

Cell Wall – Construction 1.Construction of peptidoglycan monomer. 2. Addition of pentaglycine cross-linker 3. Transglycosylation to outside of membrane 4. Transpeptidation to form cell wall (Fluit and Schmitz 2003)

Peptidoglycan Activity  See hand out for hands-on activity Dmitriev 2004

Peptidoglycan Cross-linking  Glycan chain adopts helical structure allowing the pentapeptide chains to adopt a zigzag conformation facilitating the construction of a scaffold-like cell wall structure (Dmitriev 2004)

Cell Wall – Antibiotic Target   -lactams compete with the D -Ala- D -Ala portion of peptidoglycan inhibiting cross-linking.  Bacteria fight back by degrading  -lactam ring

Vancomycin – “Drug of Last Resort”  Vancomycin is a peptide-based antibiotic produced by Amycolatopsis orientalis, a soil bacteria.  Unlike  -lactams, it cannot be administered orally but by IV.  Toxic compound which requires blood levels to be constantly monitored in the hospital.

Vancomycin Hands-on Activity  See hand out L-vancosamine D-glucose

Vancomycin - Mechanism  folds into a bowl shaped molecule  C-terminal L -Lys- D -Ala- D -Ala fits into this groove  5 hydrogen bonds are formed (Knox et al. 1990)

Vancomycin - Resistance  Naturally found in vancomycin producing bacteria as a set of 3 genes (VanA, H, and X)  Involves replacement of terminal D -Ala with D -lactate (Lessard and Walsh’s 1999)

VanX Mechanism  Zn(II)-containing metalloenzyme which removes the terminal D-Ala. (Mathews 2006)

Effect of D -Lactate  1000 fold reduction in affinity!!!  Structurally  Amine linking the D -Ala’s changes to ketone  Bonding  Eliminates a hydrogen bond  Introduces lone pair repulsion between carbonyl groups. Hands-on- Produce this molecular change in peptidoglycan and point out the changes. (Bugg et al. 1991)

Homework Assignment  Internet Research  Name one other class antibiotics  What is this class’ common target?  Sketch the molecular structure of an antibiotic from this class  Provide a brief description of the molecular geometry of this compound and how it interacts with its target molecule.

Works Cited  Bugg, Timothy; G. Wright, S. Dutka-Malen, M. Arthur, P. Courvailin, and C. Walsh. “Molecular Basis for Vancomycin Resistance in Enterococcus faecium BM4147: Biosynthesis of Depsipeptide Peptidoglycan Precursor by Vancomycin Resistance Proteins VanH and VanA.” Biochemistry 30 (1991):  Dmitriev, Boris A., Filip V. Toukach, O. Holst, E. T. Rietschel, and S. Ehlers. “Tertiary Structure of Staphylococcus aureus Cell Wall Murein.” Journal of Bacteriology 2004:7141–7148.  Lefferts, Jennifer F. “Schools trying to stay ahead of staph infections.” The Boston Globe Nov. 11, 2007: A.  Lessard, Ivan; Walsh, Christopher. “VanX, a bacterial D-alanyl-D-alanine dipeptidase: Resistance, immunity, or survival function?” Proc. Natl. Aced. Sci :  Knox, James R. and R. F. Pratt Antimicrobial Agents and Chemotherapy. 34(7) 1990:  Paustian, T, comp. Microbiology and Bacteriology: the World of Microbes Dec  Peacock, S. J., de Silva, I. & Lowy, F. D. “What determines nasal carriage of Staphylococcus aureus?” Trends Microbiol. 9 (2001):605–610.