A novel family of P-loop NTPases with an unusual phyletic distribution and transmembrane segments inserted within the NTPase domain

We predict that KAP family NTPases function principally in the NTP-dependent dynamics of protein complexes, especially those associated with the intracellular surface of cell membranes. Animal KAP NTPases, including Kidins220/ARMS, are likely to function as NTP-dependent regulators of the assembly of membrane-associated signaling complexes involved in neurite growth and development. One possible function of the prokaryotic KAP NTPases might be in the exclusion of selfish replicons, such as viruses, from the host cells. Phylogenetic analysis and phyletic patterns suggest that the common ancestor of the animals acquired a KAP NTPase via lateral transfer from bacteria. However, an earlier transfer into eukaryotes followed by multiple losses in several eukaryotic lineages cannot be ruled out.