An autoinhibitory conformation of the Bacillus subtilis spore coat protein Spo IVA prevents its premature ATP ‐independent aggregation

Spores of B acillus subtilis are dormant cell types that are formed when the bacterium encounters starvation conditions. Spores are encased in a shell, termed the coat, which is composed of approximately seventy different proteins and protects the spore's genetic material from environmental insults. The structural component of the basement layer of the coat is an exceptional cytoskeletal protein, termed Spo IVA , which binds and hydrolyzes ATP . ATP hydrolysis is utilized to drive a conformational change in Spo IVA that leads to its irreversible self‐assembly into a static polymer in vitro . Here, we characterize the middle domain of Spo IVA , the predicted secondary structure of which resembles the chemotaxis protein CheX but, unlike CheX, does not harbor residues required for phosphatase activity. Disruptions in this domain did not abolish ATP hydrolysis, but resulted in mislocalization of the protein and reduction in sporulation efficiency in vivo . In vitro , disruptions in this domain prevented the ATP hydrolysis‐driven conformational change in Spo IVA required for polymerization and led to the aggregation of Spo IVA into particles that did not form filaments. We propose a model in which Spo IVA initially assumes a conformation in which it inhibits its own aggregation into particles, and that ATP hydrolysis remodels the protein so that it assumes a polymerization‐competent conformation.