piluslike

Piluslike describes filamentous cell-surface structures that resemble pili in appearance or biogenesis but are not classified as canonical pili. The term is used when a filament is polymerized from pilin-like subunits or related proteins and is assembled by pilus assembly machinery, yet differs from true pili in composition, structure, or function.

These structures typically form long, flexible filaments extending from the cell surface. They may be made from pilin-like proteins or from proteins unrelated to canonical pilins but sharing a similar fold or assembly route. Assembly often involves dedicated secretion or assembly systems, such as ATPases and membrane platforms, which drive extrusion and polymerization outside the cell envelope.

Functions attributed to piluslike filaments include adhesion to abiotic or biotic surfaces, biofilm formation, DNA uptake for natural competence, or serving as components of secretion systems rather than direct mediators of conjugation. In some cases, they are transient or partial analogs of pili, existing mainly to position substrates or host-interaction signals.

Notable examples arise from bacteria that possess secretion systems with pilus-like extensions, such as pseudopili associated with the type II secretion system, which resemble pili but function primarily to translocate substrates. Type IV pili, while often considered true pili, are closely related and can give rise to piluslike filaments under certain conditions or in related organisms.

Because "piluslike" is a descriptive term, its exact meaning varies by study. Researchers use it to distinguish filaments that look like pili from those that are biochemically classified as pili, to emphasize differences in subunit composition, assembly, or function.