CpxA (Conjugative Plasmid Expression) is the 458 amino acid protein, a bacterial inner membrane histidine protein kinase, responsible for sensing misfolded proteins in the periplasm. It is part of CpxA/CpxR two component signal transduction system, where CpxR is the cognate response regulator. In sensing bacterial envelope stress, the Cpx pathway regulates the production of a number of periplasmic folding and trafficking factors to maintain outer membrane integrity. It is also responsible for global control of virulence factor expression. Alternative name: Integral membrane sensor signal transduction histidine kinase.