Getting organized –how bacterial cells move

proteins and DNA

Anna Buch25.01.2010

Martin Thanbichler and Lucy Shapiro

Nature Reviews, 2008

Model systems for bacterial cell biology

Box 1

• E. coli: history, genetic tools, physiology

• B. subtilis: cell differentiation, large size

• C. crescentus: cell division, synchonizable

mobile

sessile

• Diffusion and capture

Assembly of stationary protein complexes

SpoIVB

SpoIIQ

Figure 1

Mother cell

Phagocytosis-likeuptake

Septal membrane

• Targeted membrane insertion

Assembly of stationary protein complexes

SpoIVB

SpoIIIAH

SpoIIQ

Figure 1

• Targeted membrane insertion

Assembly of stationary protein complexes

Steinhauer et al., Mol Microbiol. 1999 32:367-77.; Pollard & Cooper, Science 2009 326:1208-12

IcsA: outer membrane protein, N-term is exposed to host cytoplasm

IcsP: Protease that cleaves off IcsA

Shigella flexneri:facultative intracellular pathogen

Dynamic protein scaffolds and cell shape:Bacterial actin-like cytoskeleton

Figure 2

Bundles of two or more protofilaments.

MreB dynamics in C. crescentus

Figure 2

MreB cables

Spiral like during growth

Ring-like during cell division

Architecture of MreB cables

Figure 2; Carballido-Lopez & Errington, Dev Cell. 2003 4:19-28.

B. subtilis, FRAP of GFP-Mbl

Regulation of cell-wall biosynthesis

Carballido-Lopez et al., Dev Cell. 2006 11:399-409

MreB homologues: MreBH and MblLytE: peptidoglycan hydrolase

Peptidoglycan (PG)synthetic machinery

PG-hydrolase subunit

CW binding subdomain

B. subtilis

Role of MreC in bacterial morphogenesis

Divakaruni et al., PNAS 2005 102:18602-7

C. Crescentus

PBC (penicillin-binding protein):

involved in peptidoglykan synthesis

MreC

DAPI

Crescentin

Ausmees et al., Cell. 2003 115:705-13.

C. crescentus:

creS::Tn5 -> no crescentin

creS::Tn5 + creS ->crescentin on plasmid

In-vitro assay

His-CreS filaments,

EM negative stain

Plasmid segregation

• Actin superfamiliy member (type II partitioning system)

• Walker ATPase (type I partitioning system)

• Tubulin homologue

Plasmid segregation by actin-like proteins

Figure 3

Plasmid R1 of E. coli

Plasmid segregation by Walker-type ATPases

• Walker A cytoskeletal ATPase (WACA)

Adapted from Lim et al., PNAS 2005 102:17658-63

Plasmids F and pB171 of E. coli

TubZ: B. thuringiensis serovar israelensis (pBtoxis)

Plasmid segregation by a tubulin homologue

Larsen et al., Genes Dev. 2007 21:1340-52

E.coli, expressing TubZ-GFP, FRAP, time in sec

Model proposes treadmilling

Arrangement of chromosomal DNA

Figure 4, Viollier et al., PNAS 2004 101:9257-62

Divisome: Bacterial cell-division apparatus

Allard & Cytrynbaum PNAS 2009 106:145-50; Erickson, PNAS 2009 106:9238-43

Z-ring: FitsZ filaments

Rod-shaped bacterium (e.g. E. coli)

Division-site placement: The Min system

Figure 5

minCDE operon:

MinD: WACA family

MinCD-complex: inhibit FtsZ-ring formation

MinE: represses MinCD activity

“Fail-safe mechanism”: nucleoid occlusion

B. subtilis: Noc

E. coli: SlmA

Division-site placement: The MipZ system

MipZ: ATPase, inhibits FtsZ-polymerization

ParB: chromosome partitioning protein

parS: cluster of sites, 15 kb away from ori

Conclusions

• Tubulin filaments:– cell-division apparatus, plasmid segregation

• Actin cables:– DNA partitioning, cell-shape determination,

protein localization

• WACA ATPases:– DNA segregation, cell-division plane

Outlook

• Positioning of proteins at cell poles– TipN– Peptidoglycans– Cardiolipin -> ProP

• Biochemical assembly mechanisms– Actin homologues– Tubulin homologues– WACA ATPases

Thank you for your attention!