Forms the backbone of an actin-like archaeal cytoskeleton, which is involved in cell shape determination. Has ATPase activity. Shows highest activity towards ATP or GTP as nucleotide, and only residual activity on UTP, CTP and dNTPs. Crenactin polymerization is inhibited by interaction with arcadin-2 (PubMed:27852434). Also significantly inhibited by elevated antibiotic A22 concentrations (PubMed:21414041). Monomer. The crenactin monomers polymerize into right-handed helical filaments, with 8 subunits per complete turn of the helix (PubMed:24531483, PubMed:24486010). Forms single-stranded filaments under high salt concentrations and double-stranded filaments under low salt concentrations (PubMed:26124094, PubMed:27852434). Interacts with arcadin-1 and arcadin-2 (PubMed:27852434). Forms cell-spanning helical structures. Belongs to a conserved five-gene operon within Thermoproteales denoted Arcade (actin-related cytoskeleton in Archaea involved in shape determination). Belongs to the actin family.