KDP-ATPASE OF ESCHERICHIA-COLI

Kdp-ATPase consists of three large protein subunits each having a dist inct function. The 72-kD KdpB energy-coupling subunit is homologous to other P-type ATPases, and is the site of acylphosphorylation. Evidenc e points to Asp307 as the site of phosphorylation. The 59-kD KdpA subu nit, predicted to span the membrane 12 times, appears to bind K+ for t ransport and to form the transmembrane channel for K+ movement. The 20 .5-kD KdpC subunit appears to be necessary for assembly of the complex . KdpF, a 29-residue hydrophobic peptide, is also made, but its role i s not known. Expression of Kdp is controlled at the transcriptional le vel by the 98.5-kD inner membrane-bound KdpD sensor kinase and the sol uble, cytoplasmic 2 5-kD KdpE response regulator. KdpD is autophosphor ylated and is able to transfer phosphate to KdpE. Reduced turgor press ure is believed to be the signal that stimulates the kinase activity o f KdpD to create phospho-KdpE, which in turn stimulates transcription of the operon encoding the Kdp-ATPase.