Acts as a PilB inhibitor to control natural transformation. Inhibits type IV pili (T4P) extension by specifically binding and inhibiting the pilus extension ATPase PilB but not TfpB. This activity probably modulates T4P extension under different environmental conditions. Interacts with PilB but not with TfpB. Repressed by CpiR (PubMed:34145281). Different environmental conditions may derepress cpiA to decrease pilus activity (PubMed:34145281).