parsek lecture #3

Microm 410 Fall 2009: ProkaryoticStructure/Function: Part 2/3Dr. Matt Parsek

PeptidoglycanSynthesis

Fig.6.7a

UDP-NAG

cytoplasm cell membrane cell wall

Bactoprenol-PUDP-NAM

pentapeptide

NAM-NAG

pentapeptide

Bactoprenol

PP

UMP

UMP

NAM

pentapeptide

Bactoprenol

PP

Pi

G

M

G

M

M

G

G

G

M

M

G

Interbridgepeptide


Bactoprenol-P-P

NAM‐NAG

Cross-linking of Peptidoglycan Strands

autolysins

Fig. 6.7b

Transpeptidase (FtsI)

UDP-NAG

cytoplasm cell membrane cell wall

Bactoprenol-PUDP-NAM

pentapeptide

pentapeptide

NAM-NAG

Bactoprenol

PP

UMP

UMP

NAM

pentapeptide

Bactoprenol

PP

Pi

G

M

G

M

M

G

G

G

M

M

G

Interbridgepeptide


Bactoprenol-P-P

NAM‐NAG

D-cycloserine(Oxamycin)

Bacitracin

Vancomycin

pentapeptide


Cross-linking of Peptidoglycan Strands

autolysins

Fig. 6.5

β-lactams

penicillins and cephalosporins

lysozyme

transpeptidase

Antibiotic Resistance

• Inactivate antibiotic β-lactamase (penicillinase)

Augmentin and Trimentin (combination of clavulanic acid andamoxicillin or ampicillin respectively)

• Change chemistry of target site

• Limit access of the antibiotic to target site

Clavulanic acid

CellShapeDetermination

•ModificationsmadetoPeptidoglycan:

•Protein(s)mayplayamajorrole

‐MreBprotein

‐MreB has homology to actin, a component of thecytoskeleton of eukaryotes.

‐lysozyme: Protoplasts/spheroplasts

‐autolysins

‐endopeptidase Heliobacterpylori

Bacillussubtilis

Caulobactercrescentus

Shapedeterminingprotein‐crescentin

Fig.6.4


similar predicted structures of crescentin andintermediate filaments

intermediate filaments in the bacteriaCaulobacter crescentus

Cell Wall Gram-positive Bacteria

Fig. 4.20

glycerol

StructuresofdifferentTeichoicacidsCell Wall Gram-negative Bacteria

Fig.4.23


Structure Lipopolysaccharide

Fig. 4.22

Salmonella typhimurium- ~1000 serotypes

Heptose2-keto-3-deoxyoctonic acid

MajorantigenicdetermineofGram‐negativebacteria

endotoxin Receptorssitesforcertainphage

Outer Cell Wall Proteins

• lipoproteins (Braun lipoprotein)

• porins- classical porins (non-specific channels)

OmpC- 1.1nm

OmpF- 1.2 nm

- “specific” porins

- “active transport” porin systems

Uptake of iron chelates, Vit B12, disacharides, andphosphorylated cpds

• OmpA (porin?): is essential to conjugation

LamB- maltose and maltodextrinsTsx- uptake of nucleosides

Fig.4.25

Archaealcellwalls PolysaccharidecellwallsofsomeArchaea


S‐layersaspartofthecellwall

Fig. 4.28

Capsule and Slime Layer

Streptococcus pneumoniae

Negative stain with Indiaink

Chemistry of Capsule/Slime Layer

• Polysaccharide in composition

• Glycoprotein in composition

• Protein in composition

Homopolymer of glutamic acid

Bacillus anthracis and Bacillus megaterium

Acetobacter xylinum- cellulose capsule (β-1, 4 linkage)

Agrobacterium tumefaciens- glycan capsule (β-1, 2 linkage)

Crown Gall Tumors

D-isomer

• Identifying type of capsule being made:

- chemical analysis

- serotyping Antibodies or immunoglobulinsAntigen or an antigenic determinant or epitope

E. coli- 50 different serotypes

Glycocalyx layerDextran

• Synthesized from sucrose by S. mutans;involved in plaque formation

• Polymer can also be used for:– Antithrombotic agent in microsurgery– Osmotic agents for treatment of hypovolemia– Lubricant in eye drops– Size-exclusion chromatography matrix (Sephadex)


Slime layer of carbohydrate produced by Streptococcus mutans

Dextran

Role/Function of Capsule/Slime Layer

• Attachment or adherence

Streptococcus mutans

• Protection

- desiccation

- avoiding phagocytosis

sucrose

Dental plaquebiofilm

(109 Bacteria/gram; and over 500 differentspecies identified)

In the laboratory capsule production can be deemed to be non‑essential.

Some bacteria owe theirpathogenecity to thisstructure.

Capsule/slime Layer Contributes toPathogenesis

• Streptococcus pyogenes- acute bacterial pharyngitis (sore throat)

• Streptococcus pneumoniae- pneumonia

• Yersinia pestis- plague

• Bacillus anthracis- anthrax

• Neisseria meningitidis- meningitis

parsek lecture #3

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