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Lecture 8 PMB
Fichas del conjunto (19)
- 1cytoskeletal proteinsneeded to create distinct bacterial shapes and are sometimes required for viability!!
ANALOGS TO US:
Actin = MreB
Tubulin = FtsZ
Intermediate filaments = CreS (crescentin) - 2MreBpolymerizes (using ATP) into filaments like actin; structure closely resembles actin
deplete MreB: PG synthesis continues, but is not correctly regulated --> cell wall loses shape, cell lyses
located along all of cell throughout growth and division - 3Effect of MreB/C on PBPsPBPs become mislocalized if MreB or C depleted/when MreB filaments depolymerized
- 4MreBCDform complex (PG "factories) that positions and regulates PG machinery along lateral cell walls
--> includes transglycosylases, trans-peptidases (PBP2, RodA), enzymes that make PG monomers (MraY, MurG)
without MreBCD: PBP2 mislocalized -->
lateral cell walls not made normally --> cells become swollen and lyse - 5How does MreB mobilize around the cell?Driven by the synthesis of PG:
MreB associates with the PBP complex
via lipid-linked PG precursors (products of MurG and MraY)
Without precursors: MreB disassembles, no movement cause by PG synthesis - 6Crescentin (CreS)responsible for the curved shape of Caulobacter/etc; similar to intermediate filaments
- 7What does curvature mean for the cell?Curved cells have an advantage in surface attachment under flow cytometry conditions --> better access to nutrients
- 8How does curvature help with surface attachment?curved cells attach to surfaces w/ polar stalk & holdfast at tip --> during growth, pili built at pole opposite the stalk --> new pili stick to surface --> at division the new daughter cell is already attached
curved cells have the advantage because new pili points down (unlike for straight)! - 9What proteins act at the division site to form a new septa?WT FtsZ: forms ring at site of cell division between the two replicated chromosomes
- 10FtsZhelps with cell division and septa formation
tubulin homolog; filaments of this form a Z ring that constricts to drive cell devision
assembly site for the divisome - 11divisomelarge protein complex that spans IM + synthesizes septal cell wall!
subunits are essential for viability; studied using ts mutations or depletion
-FtsA & ZipA: tether FtsZ to the membrane
-FtsW: PBP3 --> septum; transglycosylase
-FtsK: chromosome segregation
-FtsQLB: triggers Z-ring & cell constriction - 12What drives the motion of PBPs at the septum?FtsZ treadmilling (building concentric rings moving inward over time)
FtsZ GTPase activity blocked --> PBPs stop moving around circumference - 13How does FtsZ cause circular constriction at division site?1) FtsZ GTPase activity: FtsZ-GDP filaments are bent from original FtsZ-GTP
2) FtsZ-GDP anchored to the cytoplasmic membrane --> PBPs build PG along a bent/curved path
3) FtsZ treadmills in curved paths at division site --> drives the motion of PBPs! - 14minCDE mutantnormal cells,
long rods, and
minicells
central AND polar division sites used - 15minE mutantlong filaments
minCD blocks division everywhere - 16MinC and MinDRapid pole-to-pole oscillation
MinC and MinD form “tube” on cytoplasmic membrane at one end of the cell --> every
20s, migrate to the opposite pole - 17Min EMinE forms ring at edge of MinCD zone.
E ring moves toward pole containing MinCD --> MinC and MinD are released --> set up a new polar zone at the other end,
away from MinE - 18mechanism for Min Oscillation1) MinC bound to MinD --> MinC shortens + inhibits FtsZ filaments bundling
2) MinD-ATP binds IM, carries MinC with it
--> hydrolyzes ATP --> released from IM
3) MinE binds to MinD and IM --> MinE stimulates ATPase activity of MinD --> releases MinCDE from membrane.
5) MinE rapidly rebinds to the membrane (and itself), near where it just fell off.
6) In cytoplasm, MinD exchanges ADP for ATP --> rebinds to the membrane (if near MinE: expelled from the membrane; if far from MinE set up a new zone of MinCD
7) Net result: is that MinC, the FtsZ inhibitor, spends most time at cell poles and very little time at the midcell!! - 19nucleoid occlusionnucleoid gives off a signal preventing FtsZ ring formation nearby
EX: SlmA binds to SBS in E. coli genome;
SBS NOT present near terminus (located
in center of cell near division plane);
SlmA + SBS inhibits FtsZ polymerization, but SlmA alone does not