Week 5: Introduction to antibiotics - PENICILLIN mechanism of action

Question 1

Gram-positive bacteria have a thicker peptidoglycan, what else is a feature?

Answer 1

decorated with glycans structures, Lipoteichoic acid (LTA)

single plamsa membrane

Question 2

What is Lipoteichoic acid (LTA)?

Answer 2

a surface-associated adhesion amphiphile from Gram-positive bacteria and regulator of autolytic wall enzymes (muramidases). It is released from the bacterial cells mainly after bacteriolysis induced by lysozyme, cationic peptides from leucocytes, or beta-lactam antibiotics.

Question 3

What is single plasma membrane also called?

Answer 3

lipid bilayer

Question 4

What can the plasma membrane sometimes carry?

Answer 4

porins

Question 5

What is the role of porins in the plasma membrane?

Answer 5

facilitate uptake of compounds

beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse.

Question 6

What is an example of something giving the Gram-negative bacteria negative charge?

Answer 6

lipopolysaccharides

Question 7

Why are some drugs Gram-positive/negative specific?

Answer 7

the different structural components require a different antibiotic to be able to penetrate the cell wall/ peptidoglycan

Question 8

What has happened to penicillin-sensitive diseases?

Answer 8

more have become insensitive to penicillin antibiotics

Question 9

What 2 sugars make up peptidoglycan?

Answer 9

Glcnac
Anh Murnac

Question 10

What are the alternating sugars connected by in the peptidoglycan layer?

Answer 10

The alternating sugars are connected by a β-(1,4)-glycosidic bond.

Question 11

Do humans have the NagZ and LT?

Answer 11

no

Question 12

What is the supportive side chain of the peptidoglycan?

Answer 12

D-ala
L-ala

Question 13

What links the side chains of the peptidoglycan sugars?

Answer 13

PBP transpeptidation

penicillin binding protein

Question 14

What is the process of linking the peptides side chains of the peptidoglycan together?

Answer 14

transpeptidation

Question 15

What stain of bacteria can penicillin treat?

Answer 15

both + and -

Question 16

Does penicillin have a similar structure to the D-Ala-D-Ala peptide side chain structure of the peptidoglycan?

Answer 16

yes

Question 17

What structure does penicillin have?

Answer 17

beta-lactam

Question 18

What does beta-lactam moiety mimic in penicillin?

Answer 18

the intermediate

the natural D-Ala-D-Ala substrate of the family of enzymes known as penicillin-binding proteins (PBP), which are responsible for cross-linking the peptidoglycan component of the bacterial cell wall.

Question 19

What is the peptide biding protein in S. aureus?

Answer 19

PBP2a

Question 20

What class of enzyme is PBP?

Answer 20

transpeptidase

Question 21

What does PBP do?

Answer 21

cleave of the D-ala-D-ala

The cross-link is one peptide short, missing the final D-ala

cleaves off and link to the seconds peptide strand.

links the d-ala-d-ala

Question 22

Where does the PBP2a bind the side chain?

Answer 22

d-ala bonds into the active site of S. aureus PBP2a.

Question 23

What process of PBP2a involved in?

Answer 23

tranpeptdase cross-linking

Question 24

What 2 residues does the PBP2a use?

Answer 24

ser (hydroxyl) and Lys (amide) sidechains

Question 25

What are the ser and Lys residues called?

Answer 25

catalytic residues

Question 26

What is the role of the ser the PBP2a?

Answer 26

d-ala bonds to the ser in the active ste and the ser residue performs a nucleophilic attack.

attacks the bond between the peptide

reshuffle electron, electrons move and H+ released.

covalent bond formed between the terminal d-ala and serine residue.

The peptide chain gains the =O from the serine and the serine now has an -OH.

new peptide formed.

Question 27

What is the role of Lys in the transpeptidase cross-linking?

Answer 27

create a positive environment

Question 28

How does penicillin interfere with the transpeptidase cross-linking process?

Answer 28

takes away the binding site of the d-ala-d-ala

In the bound state, still have ser and lys residue

The penicillin is able to mimic the d-ala-d-ala.

ser thinks that the carboxyl group is form a peptide group, it tries to attack and cleave it.

Now it can form the covalent intermediate.

Question 29

Hoe does transpeptidase cross-linking and penicillin inhibition differ?

Answer 29

when the penicillin-ser covalent intermediate is made.

the penicillin is now contently linked to the ser and not the peptide, which normally gets re-cleaved.

Question 30

Why can penicillin covalantly bond to the ser and not be re-cleaved?

Answer 30

the bulky beta-lactam

can attack the covalent bond.

Question 31

How can a cell survive agianst penicillin?

Answer 31

produce more and more transpeptidase in order to out compete the penicillin

Question 32

Does penicillin enter the cell?

Answer 32

no just sits outside

Question 33

How does penicillin kill?

Answer 33

penicillin kills by interfering with the production of cell wall - as these e.coli grow in size, the weakened cell wall ruptures

stop the remodeling process and peptidoglycan

the osmotic pressure increases and the cells burst open.

Question 34

What drugs share the beta-lactam ring?

Answer 34

cephalosprorins, carbapenems and monobactams