MRSA Treatment andMolecular 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.

20-40 nm thick Composed of

Peptidoglycans Teichoic acids Surface proteins

(Todar 2005)

Cell Wall – Construction

1. Construction ofpeptidoglycan monomer.2. Addition ofpentaglycine cross-linker3. Transglycosylationto outside of membrane4. Transpeptidation toform 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

http://sitemaker.umich.edu/medchem9/penicillin_pharmacology

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

CH3

CH3NH2

O

NHNH

O

OH

NH2

O

O

NHNH

O

NH

O

O

NH

OH

OHO

a.

Leucine

Tyrosine

AsparagineLeucine

Glycines

Tyrosine

H

H

ClO

O O

NH

OH

Cl

NH

O

NH

ONH

O

OHOHOH

OH

O

NH

NH2

O O

NH

OH

O

NH

H

CH3

CH3

CH3

O

O

OOH

OHOH

CH3

OH

NH2

CH3

OH

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

Cl O O O

N H

O H

Cl

N H O N H

O N H O

O H O H

O H

O H

O

N H

N H 2

O O

N H O H

O N H C H 3

C H 3

C H 3

O

O

O O H O H

O H

C H 3 O H N H 2 C H 3

O H

O N H 2

N H 2

N H O

C H 3 N H

O

C H 3 O -

(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 antibioticsWhat is this class’ common target?Sketch the molecular structure of an antibiotic

from this classProvide 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):10408-10415.

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. 96 1999:11028-11032.

Knox, James R. and R. F. Pratt Antimicrobial Agents and Chemotherapy. 34(7) 1990:1342-1347. Paustian, T, comp. Microbiology and Bacteriology: the World of Microbes. 2006. 31 Dec. 2007

http://www.bact.wisc.edu/Microtextbook/index.php?module=Book&func=displayarticle&art_id=137.

Peacock, S. J., de Silva, I. & Lowy, F. D. “What determines nasal carriage of Staphylococcus aureus?” Trends Microbiol. 9 (2001):605–610.