G+ cell wall

Question 1

Sugar/Glycan component of Peptidoglycan

Answer 1

Basic units are NAG and NAM

-joined by ß-1,4 glycosidic linkages into long backbone chains

Question 2

NAG = ?

Answer 2

N-acetyl-D-glucosamine

*also: GlcNAc

Question 3

NAM = ?

Answer 3

N-acetyl-D-muramic acid

*also: MurNAC

Question 4

ß-1,4 glycosidic linkages are susceptible to what?

Answer 4

Lysozyme

-positively charged protein found in many human secretions

Question 5

What kind of peptide is in peptidoglycan?

Answer 5

A tetra peptide

Question 6

The main difference between tetra peptides of gram + and gram - is?

Answer 6

The third amino acid

Question 7

4 amino acids in the gram + tetrapeptide

Answer 7

L-ala-D-glu-L-lys-D-ala.

Question 8

The tetra peptide is linked to which glycan in the backbone?

Answer 8

NAM

Question 9

What is the 3rd amino acid for gram positive bacteria (like S. aureus)

Answer 9

L-lys

Question 10

What is the 3rd amino acid for gram negative bacteria (like E. coli)

Answer 10

mesoDap = D,L-diaminopimelic acid

Question 11

Direct cross linking of glycan chains by the tetrapeptide occurs in

Answer 11

Gram negative cells

Question 12

Cross linking via a cross bridge occurs in?

Answer 12

Gram positive cells

Question 13

What is the typical link between the tetrapeptides in direct linking

Answer 13

via a peptide bond between the amino group of dap or lys and the D-ala C-terminus.

Question 14

What are the 3 stages of peptidoglycan synthesis

Answer 14

1. Cytoplasmic steps
2. Membrane associated steps
3. Cell wall steps

Question 15

5 parts in the cytoplasmic step of peptidoglycan formation

Answer 15

1. NAG is activated by combining it with UDP
2. Conversion of UDP-NAG to UDP-NAM (inhibited by phosphomycin)
   - 1st committed step?
3. Enzymatic addition of 5 amino acids of which the last dipeptide is D-ala-D-ala
   - addition of D-ala dipeptide is inhibited by cycloserine
4. Transfer of the UDP-NAM pentapeptide (aka. Park’s nucleotide) to a membrane bound carrier lipid
   * *this forms Lipid I

Question 16

Why is phosphomycin a bad antibiotic ?

Answer 16

Toxic to humans and bacteria can easily develop resistance to it

Question 17

how is the D-ala dipeptide formed?

Answer 17

By an alanine racemase which turns the natural L-ala into the unusual D-ala
-makes it a great target for antibiotics

Question 18

3 parts in the membrane step of peptidoglycan synthesis

Answer 18

1. Lipid I from the cytoplasmic step is turned into Lipid II by the formation of a ß-1,4 link between NAG and NAM (still on the carrier lipid)
2. The pentapeptide is then modified (occurs in a species specific way)
3. The disaccharide unit is transferred from the lipid carrier to the backbone chain by transglycosylation

Question 19

Which 2 drugs can inhibit transglycosylation

Answer 19

Vancomycin and Ristoceitin

Question 20

What is C55-P

Answer 20

A hydrophobic lipid carrier used to attach the pentapeptide to the membrane and helps transport the peptidoglycan precursor to the outer part of the membrane

Question 21

2 cell wall steps in peptidoclycan synthesis

Answer 21

1. Formation of peptide crosslinks by transpeptidation

2. Removal of the terminal D-alanine on the pentapeptide by a carboxy-peptidase

Question 22

Which class of antibiotics inhibits transpeptidation (formation of peptide cross links)

Answer 22

Penicillins

Question 23

What is transglycosylation

Answer 23

transfer of a sugar residue from one glycoside to another

Question 24

Describe the method of vancomycin activity

Answer 24

Vancomycin binds to the terminal D-ala-D-ala of the pentapeptide. The binding prevents transglycosylation (and to a certain extent transpeptidation) to occur.

*this is because vancomycin is a very bulky antibiotic and can effectively block the bacterial enzyme

Question 25

Name one way in which bacteria can become resistant to vancomycin

Answer 25

By using a different terminal dipeptide | -vancomycin will only recognize D-ala-D-ala

Question 26

Bacitracin - effect

Answer 26

Blocks release of Pi from lipid carrier [undecaprenyl-PP ---> undecaprenyl-P + Pi] -prevents the lipid carrier from reforming *toxic so it is only used topically in things like polysporin

Question 27

Phosphomycin action

Answer 27

Inhibits MurA --> formation of UDP-NAM is prevented.

Question 28

Cycloserine action

Answer 28

Competitive inhibitor of the D-alanine racemase and D-ala-D-ala synthetase. Blocks synthesis of D-ala-D-ala.

Question 29

Penicillins action

Answer 29

aka. ß-lactams Inhibit penicillin-binding proteins, prevent transpeptidation

Question 30

Bacteria may contain up to __ different penicillin binding proteins

Answer 30

8

Question 31

What are the 3 high MW PBPs

Answer 31

PBP1, 2, and 3

Question 32

what is the role of the high MW PBPs

Answer 32

catalyze transglycosylation and transpeptidation reactions in peptidoglycan synthesis

Question 33

PBP3 is specifically required for?

Answer 33

Peptidoglycan synthesis in the septum

Question 34

What are the 3 low MW PBPs?

Answer 34

PBP 4, 5, and 6

Question 35

What is the role of the low MW PBPs?

Answer 35

appear to be dispensible

Question 36

Alterations in the the PBPs can lead to what kind of resistance ?

Answer 36

Non β-lactamase β-lactam antibiotic resistance | -resistance to penicillins without having the β-lactamase enzyme

Question 37

β-lactamase

Answer 37

Enzyme which degrades the ß-lactam ring on penicillins

Question 38

3 types of cell wall hydrolases

Answer 38

Also called autolysins: N-acetylglucosaminidase, N-acetylmuramidase, endopeptidases

Question 39

N-acetylglucosaminidase and N-acetylmuramidase work by....?

Answer 39

Cutting the glycan backbone of the peptidoglycan via lysozome action

Question 40

Endopeptidases work by?

Answer 40

Cutting the peptide links (in the crossbridges?)

Question 41

3 roles of autolysins

Answer 41

1. Essential for cell division 2. Required for morphogenesis and turnover - inserting new peptidoglycan into the cell wall 3. DNA release and biofilm formation - those things can only be released if the cell wall is cut

Question 42

similarities in the structure of LTAs and TAs

Answer 42

Both are polymers of glyerol or ribitol phosphates | -common to have substitution groups like NAG or D-ala

Question 43

TA linking

Answer 43

TAs are covalently linked to the peptidoglycan | -linkage is via a unit made of sugar residues

Question 44

LTA linking

Answer 44

LTAs have glycolipids which allows them to anchor to the cell membrane -anchored to the outer leaflet

Question 45

6 biological functions of LTA and TA

Answer 45

1. Facillitate adhesion - helps in colonization 2. Capture divalent cations 3. Binding site for some enzymes that can cleave peptidoglycan 4. Activate complement 5. Confer resistance to cationic antimicrobial peptides 6. Activate innate immune response - induce cytokine production

Question 46

D-ala substitutions plan an important role in which functions of LTA and TA?

Answer 46

Resistance to antimicrobial peptides and activation of the innate immune response

Question 47

Explain the role of D-ala substitutions in resistance to antimicrobial peptides

Answer 47

D-ala substitutions make the LTA more positively charged This increased positive charge repels cationic antimicrobial peptides -CAMPS insert into the cell membrane and cause cell death

Question 48

Explain the role of D-ala substitutions in immune recognition

Answer 48

TLR 2 is involved? WHAT IS IMPORTANT ABOUT THIS?

Question 49

Surface proteins can be associated with the cell wall by

Answer 49

Non covalent or covalent bonds

Question 50

4 examples pf LPXTG proteins

Answer 50

Collagen adhesion protein Iron binding proteins -Critical for survival where iron is limited Cell surface pilins (in the pili) Protein A -Binds to Fc terminus of human immunoglobulins in a non-immune fashion

Question 51

LPXTG proteins have a C-terminal.....

Answer 51

Sorting sequence in the protein It is a ~35aa stretch encompassing a conserved LPXTG motif (X is any amino acid) Proteins are amide-bonded to the peptide cross-bridge of peptidoglycan by an enzyme called sortase. Sortase is a transpeptidase and cleaves between the T and the G