Lecture 8: Bacterial Cytoskeleton
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What are the 4 bacterial cytoskeletal elements?
• Tubulin homologue - FtsZ • Actin homologue - MreB, Mbl proteins; ParM, MamK • Intermediate filaments - CreS • Molecular motors - not found in bacteria yet
What is the role of MreB (and Mbl) in bacteria? actin homologue
• Cell growth and shape • mreB - mecillinam resistance gee identified in E. coli (rod) • mreB mutants = spherical • mbl mutants = deformed
What happens to MreB in the presence of ATP or GTP?
• Polymerases into filaments • Either form a continuous helical arrangement or dynamic patch arrangement
How does MreB direct cell shape?
• “Localizing proteins in a peptidoglycan factory” • MreC required for spatial organization of components of the peptidoglycan synthesis holoenzyme in the periplasm • MreB directs localization of precursor synthesis proteins in the cytosol
How does MreB correlate with cell shape?
1. Spherical bacteria have be seen to have no MreB gene 2. Rod bacteria do have MreB gene a. HOWEVER TWO GROUPS DO NOT: Agrobacteriuml Rhizobacterium Mycobacteriuml Corynebacterium
Where in the cell does the wall grow from in rod shaped bacteria?
• MOST cells: from the middle of the ‘long wall’ (MreB CABLES PRESENT) • EXCEPTIONS: at the poles (NO MreB PRESENT)
What does FtsZ control (tubulin homologue)?
Cell division
What is FtsZ polymerase dependent on?
GTP
How is a FtsZ ring formed
assembly of numerous polymers using accessory proteins
What is the process of binary fission?
• growth/extension • chromosome replication • chromosome segregation • making the division site - crosswall formation • cell-cell seperationn
How does FtsZ create cell division?
• FtsZ polymerizes into ring structure in presence of GTP (GTPase activity) • FtsZ recruits other proteins (some involved in synthesis of new cell wall at division site) • Alongside extension at the long side of the cell in rod bacteria, extension also occurs in the middle of the division site using FtsZ as a scaffold
How do spherical bacteria extend their cell wall?
Only occurs at the division site of the cell
What is the role of intermediate filaments in bacteria?
• CreS (IF) • CreS mutants lose the curved shape • CreS forms a filament alongside the curved shape of Caulobacter cells
What is the role of ParM (actin homologue)?
• Plasmid Positioning • (much like the mechanism used in eukaryotes using microtubules during mitosis)
What is the role of MamK (actin homologue)?
controls organization of magnetite particles in magnetosomes