tailieunhanh - Báo cáo khoa học: The sensor protein KdpD inserts into the Escherichia coli membrane independent of the Sec translocase and YidC

KdpD is a sensor kinase protein in the inner membrane of Escherichia colicontaining four transmembrane regions. The periplasmic loops connecting the transmembrane regions are intriguingly short and proteasemapping allowed us to only follow the translocation of the second periplasmic loop. The results show that neither the Sec translocase nor theYidCprotein are required formembrane insertion of the second loop ofKdpD. | Eur. J. Biochem. 270 1724-1734 2003 FEBS 2003 doi The sensor protein KdpD inserts into the Escherichia coli membrane independent of the Sec translocase and YidC Sandra J. Facey and Andreas Kuhn Institute of Microbiology and Molecular Biology University of Hohenheim Stuttgart Germany KdpD is a sensor kinase protein in the inner membrane of Escherichia coli containing four transmembrane regions. The periplasmic loops connecting the transmembrane regions are intriguingly short and protease mapping allowed us to only follow the translocation of the second periplasmic loop. The results show that neither the Sec translocase nor the YidC protein are required for membrane insertion of the second loop of KdpD. To study the translocation of the first periplasmic loop a short HA ei iilope tgg was geeelically introduced into this region. The results show that also the first loop was translocated independently of YidC and the Sec translocase. We conclude that KdpD resembles a new class of membrane proteins that insert into the membrane without enzymatic assistance by the known translocases. When the second periplasmic loop was extended by an epitope tag to 27 amino acid residues the membrane inser tion of this loop of KdpD depended on SecE and YidC. To test whether the two periplasmic regions are translocated independently of each other the KdpD protein was split between helix 2 and 3 into two approximately equal-sized fragments. Both constructed fragments which contained KdpD-N residues 1-448 of KdpD and the KdpD-C residues 444-894 of KdpD readily inserted into the membrane. Similar to the epitope-tagged KdpD protein only KdpD-C depended on the presence of the Sec translocase and YidC. This confirms that the four transmembrane helices of KdpD are inserted pairwise each translocation event involving two transmembrane helices and a periplas-mic loop. Keywords Escherichia coli membrane protein protein translocation epitope tag. The inner membrane