The actin cytoskeleton in prokaryotic cells is functionally similar to which of the following eukaryotic proteins?
Prokaryotic cells maintain rod shape and organize cell wall synthesis without eukaryotic compartments using cytoskeletal homologs sharing ancient ATPase fold. MreB, belonging to actin Hsp70 superfamily, shares structural core of five conserved sequence motifs forming ATP binding pocket between domains IA and IIA. Purified MreB polymerizes into ATP dependent antiparallel double filaments that rotate circumferentially beneath cytoplasmic membrane driven by cell wall elongation machinery. It scaffolds elongasome complex containing RodA glycosyltransferase, PBP2 transpeptidase and MreC MreD, directing insertion of new peptidoglycan hoops to maintain lateral wall. Depletion or inhibition by small molecule A22 causes rod to sphere transition confirming morphogenetic role, similar to actin controlling shape in eukaryotes. Keratin and vimentin are metazoan intermediate filament proteins absent in most bacteria and archaea, while ActA is Listeria monocytogenes surface protein that activates host Arp2/3 complex to form actin comet tails for motility, not bacterial cytoskeleton. Thus prokaryotic actin analog best matching functional criteria is MreB protein.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton and Bacterial Homologs MreB.