The stoichiometry of minor-to-major pilins regulates the dynamic activity of the type IVa competence pilus in

Type IVa pili (T4aP) are bacterial surface appendages that perform various functions including twitching motility, surface attachment, cell-cell interactions, and DNA uptake for natural transformation. Pivotal to each of these functions is the ability of T4aP to be dynamically extended and retracted from the cell surface. However, the factors that regulate this dynamic activity remain poorly understood. To address this question, we employ the competence T4aP from AUTHOR SUMMARY: Type IVa pili (T4aP) are a broadly conserved family of filamentous bacterial appendages that help bacteria colonize surfaces, move towards or away from stimuli, and gain new traits through a mechanism of horizontal gene transfer called natural transformation. T4aP are primarily composed of protein subunits called major and minor pilins, named based on their relative abundance in the pilus filament. Bacteria can dynamically extend and retract pilus filaments from their surface through polymerization and depolymerization of these pilins. This dynamic activity is critical for the activities that T4aP carry out. However, the factors that regulate this dynamic activity remain incompletely understood. Here, we find that the ratio of minor-to-major pilins is one factor that regulates the frequency of dynamic activity. Minor pilins are a universally conserved feature of T4aP. So, the minor-to-major pilin ratio may be a broadly conserved mechanism for controlling dynamic T4aP activity in diverse bacterial species.