Btubulin

BTubulin refers to bacterial tubulin, a set of prokaryotic homologs of the eukaryotic tubulin family. The best characterized examples are BtubA and BtubB, proteins found in certain bacteria such as Prosthecobacter. These BtubA/B proteins are considered tubulin-like and share structural features with eukaryotic tubulins, indicating a common ancestry within the tubulin superfamily.

Biochemical and structural features: BtubA and BtubB Form a heterodimer that binds and hydrolyzes GTP. They polymerize into filamentous structures that resemble protofilaments associated with microtubules, and their assembly is nucleotide-dependent and Mg2+-assisted. In vitro studies show that BtubA/B can generate microtubule-like polymers and that polymerization is regulated by the GTP-bound state. Some species also have additional interacting proteins, such as BtubC, that influence filament dynamics.

Distribution and function: BtubA/B have been identified in a limited set of bacteria, most notably Prosthecobacter and related taxa. They are not widespread across bacterial lineages. The precise in vivo function of Btubulin-based filaments remains an area of active research; proposed roles include contributions to cell shape maintenance, subcellular organization, and possibly processes analogous to intracellular transport, though clear physiological assignments are not yet established.

Evolutionary significance: The existence of BtubA/B provides insight into the evolution of the cytoskeleton, suggesting that tubulin-like elements existed in diverse lineages prior to the emergence of the eukaryotic cell. The evolutionary origin of Btubulin is debated, with hypotheses ranging from vertical inheritance in a restricted lineage to ancient paralogy or horizontal transfer events.

See also: Tubulin, Microtubule, BtubA, BtubB, bacterial cytoskeleton.