Diversification and functional expansion of archaeal TFF machineries

Archaea have several cell surface structures that belong to the type 4 filament (TFF) superfamily. What all have in common is the presence of core minimal assembly systems consisting of an ATPase, a platform protein, a filament forming protein and a class III signal peptidase. Here we generated novel MacSyFinder2 models to identify and classify archaeal TFF systems. Our analysis revealed a vast diversity of archaeal TFF with several members harboring one or more TFF assembly machineries. Structure-based phylogenetic analyses revealed that the variable N-terminal domain of TFF-related ATPases reflects the subsystem clustering. This indicates a diversification of the core machinery components within the archaeal secretion ATPase family driven through structural innovation. Genome-wide screening of SP-III containing proteins revealed the widespread presence of substrate binding proteins with SPIII. We hypothesize that these binding proteins with canonical SPIII cleavage sites are used to functionalize TFF machineries for efficient substrate scavenging, expanding the functional repertoire of archaeal TFF systems beyond currently characterized roles.