Practice question

Bacterial shape determination relies on diverse cytoskeletal filaments beyond tubulin homolog FtsZ and actin homolog MreB, allowing morphological complexity. Crescent-shaped morphology characteristic of Caulobacter crescentus and related alphaproteobacteria depends directly on filament-forming protein called crescentin, encoded by creS gene, which is structurally analogous to eukaryotic intermediate filament proteins such as lamins and keratins, featuring long central coiled-coil domain. Crescentin assembles spontaneously into 10 nanometer wide filaments without requiring nucleotide hydrolysis and attaches to membrane along inner concave curvature via membrane protein CTP synthase anchoring, imposing mechanical strain that biases peptidoglycan insertion toward outer side, thus creating persistent curvature maintained through growth. Mutants lacking crescentin become straight rods, while heterologous expression of crescentin in otherwise straight Escherichia coli imparts curvature, demonstrating sufficiency and modularity. In contrast, FtsZ drives septal peptidoglycan synthesis at midcell during division, ParM is actin-like protein forming dynamic filaments that push plasmids apart via polymerization-based motility. Therefore crescent morphology specifically depends on crescentin rather than division or plasmid partitioning proteins.