Retraction ATPase Motors from Three Orthologous Type IVa Pilus Systems Support Promiscuous Retraction of the Vibrio cholerae Competence Pilus.

Bacterial 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 three orthologous T4aP can functionally complement Vibrio cholerae mutants that lack their endogenous motors. We found that the PilT and PilU retraction ATPases from the three T4aP systems tested are promiscuous and promote the retraction of the V. cholerae competence T4aP despite a high degree of sequence divergence. In contrast, the orthologous extension ATPases from the same T4aP systems were not able to mediate the extension of the V. cholerae competence T4aP despite exhibiting a similar degree of sequence divergence. Also, we show that one of the PilT orthologs characterized does not support PilU-dependent retraction and provide some data to indicate that the C terminus of PilT is important for PilU-dependent retraction. Together, our data suggest that retraction ATPases may have maintained a high degree of promiscuity for promoting the retraction of T4aP, while extension ATPases may have evolved to become specific for their cognate systems.