Topological analysis and role of the transmembrane domain in polar targeting of PilS, a Pseudomonas aeruginosa sensor kinase

In Pseudomonas aeruginosa, synthesis of pilin, the major protein subunit of the pill, is regulated by a two-component signal transduction system in wh ich PilS is the sensor kinase, PilS is an inner membrane protein found at t he poles of the bacterial cell. It is composed of three domains: an N-termi nal hydrophobic domain; a central cytoplasmic linker region; and the C-term inal transmitter region conserved among other sensor kinases. The signal th at activates PilS and, consequently, pilin transcription remains unknown. T he membrane topology of the hydrophobic domain was determined using the lac Z and phoA gene fusion approach. In this report, we describe a topological model for PilS in which the hydrophobic domain forms six transmembrane heli ces, whereas the N- and C-termini are cytoplasmic, This topology is very st able, and the cytoplasmic C-terminus cannot cross the inner membrane. We al so show that two of the six transmembrane segments are sufficient for membr ane anchoring and polar localization of PilS.