Retraction ATPase motors are promiscuous among type IVa pilus systems

Abstract

ABSTRACTBacterial surface appendages called type IVa pili (T4aP) promote diverse activities including DNA uptake, twitching motility, and virulence. These activities rely on the ability of T4aP to dynamically extend and retract from the cell surface. Dynamic extension relies on a motor ATPase commonly called PilB. Most T4aP also rely on specific motor ATPases, commonly called PilT and PilU, to dynamically and forcefully retract. Here, we systematically assess whether motor ATPases from 4 distinct T4aP could functionally complement Vibrio cholerae mutants that lacked their endogenous motors. We found that the retraction ATPases PilT and PilU are highly promiscuous and promote retraction of the V. cholerae competence T4aP despite a high degree of sequence divergence. In contrast, orthologous extension ATPases were not able to mediate extension of the V. cholerae competence T4aP despite a similar degree of sequence divergence. Also, we show that one of the PilT orthologs characterized does not support PilU-dependent retraction and we attributed this loss of activity to the 3’ end of the gene, which suggests that the C-terminus of PilT plays an important role in promoting PilU-dependent retraction. Together, our data suggest that retraction ATPases have maintained a high degree of promiscuity for promoting retraction of diverse T4aP, while extension ATPases have evolved to become highly specific for their cognate systems.IMPORTANCEOne way that bacteria interact with their environments is via hair-like appendages called type IVa pili (T4aP). These appendages dynamically extend and retract from the cell surface via the action of distinct ATPase motors. T4aP are present in diverse bacterial species. Here, we demonstrate that retraction motors from T4aP are highly promiscuous, and capable of promoting retraction of heterologous T4aP systems. By contrast, extension ATPase motors are highly specific and cannot promote extension of heterologous T4aP. Thus, these results suggest that T4aP extension may be more tightly regulated compared to T4aP retraction.