Reformulation of an extant ATPase active site to mimic ancestral GTPase activity reveals a nucleotide base requirement for function

Hydrolysis of nucleoside triphosphates releases similar amounts of energy. However, ATP hydrolysis is typically used for energy-intensive reactions, whereas GTP hydrolysis typically functions as a switch. SpoIVA is a bacterial cytoskeletal protein that hydrolyzes ATP to polymerize irreversibly during Bacillus subtilis sporulation. SpoIVA evolved from a TRAFAC class of P-loop GTPases, but the evolutionary pressure that drove this change in nucleotide specificity is unclear. We therefore reengineered the nucleotide-binding pocket of SpoIVA to mimic its ancestral GTPase activity. SpoIVA(GTPase) functioned properly as a GTPase but failed to polymerize because it did not form an NDP-bound intermediate that we report is required for polymerization. Further, incubation of SpoIVA(GTPase) with limiting ATP did not promote efficient polymerization. This approach revealed that the nucleotide base, in addition to the energy released from hydrolysis, can be critical in specific biological functions. We also present data suggesting that increased levels of ATP relative to GTP at the end of sporulation was the evolutionary pressure that drove the change in nucleotide preference in SpoIVA.

Automated summary

Hydrolysis of nucleoside triphosphates releases similar amounts of energy, with ATP typically used for energy-intensive reactions and GTP serving as a switch. The bacterial cytoskeletal protein SpoIVA, evolved from a TRAFAC class of P-loop GTPases, failed to polymerize after reengineering its nucleotide-binding pocket to mimic ancestral GTPase activity, highlighting the critical role of the nucleotide base in specific biological functions. The evolutionary pressure that drove the change in nucleotide preference in SpoIVA was suggested to be increased levels of ATP relative to GTP at the end of sporulation.