Part of the binding-protein-dependent transport system for phosphate; probably responsible for the translocation of the substrate across the membrane. The complex is composed of two ATP-binding proteins (PstB), two transmembrane proteins (PstC and PstA) and a solute-binding protein (PstS). Transcription slightly induced by phosphate starvation, part of the pstB3-pstS2-pstC1-pstA2 operon (PubMed:20933472). Belongs to the binding-protein-dependent transport system permease family. CysTW subfamily.