Regulation of Sulfolobus acidocaldarius surface structures by the PP2A core interaction module

Protein phosphorylation is a central regulatory mechanism that enables organisms to adapt to changing environmental conditions. The hyperthermophilic archaeon Sulfolobus acidocaldarius encodes only two phosphatases: the dual-specificity phosphatase PTP and the serine/threonine phosphatase PP2A. PP2A has previously been implicated in archaellum regulation, and its deletion results in a hypermotile phenotype. Under starvation conditions, PP2A associates with a stress regulatory module comprising the archaellum repressors ArnA and ArnB, the universal stress protein UspA, and a GPN-loop GTPase. Here, we investigated PP2A-associated proteins under normal growth conditions and following UV-induced DNA damage. Pulldown experiments using a genomically HA-tagged PP2A strain identified a PP2A-associated basal regulatory module consisting of ArnA, ArnB, ArnE, and PTP, distinct from the previously described starvation-associated network. In addition, several proteins involved in the biogenesis and regulation of type IV pili co-purified with PP2A. Functional analyses using thermomicroscopy and electron microscopy revealed that deletion of {Delta}pp2a, {Delta}arnA, or {Delta}arnB abolishes Aap-pilus formation and twitching motility, demonstrating that the PP2A regulatory network controls both swimming and surface-associated motility. In contrast, the same network exerted only a modulatory effect on UV-induced cell aggregation. Together, our findings establish PP2A as a central regulator coordinating multiple archaeal surface structures through phosphorylation-dependent signaling.