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  • The EMBO Journal (1998) 17, 2504 - 2512
  • doi:10.1093/emboj/17.9.2504

The Escherichia coli SRP and SecB targeting pathways converge at the translocon

Quido A. Valent1, Pier A. Scotti1, Stephen High2, Jan-Willem L. de Gier3, Gunnar von Heijne3, Georg Lentzen4, Wolfgang Wintermeyer4, Bauke Oudega1 and Joen Luirink1

  1. Department of Microbiology, Institute of Molecular Biological Sciences, Biocentrum Amsterdam, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
  2. School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK
  3. Department of Biochemistry, Stockholm University, S-106 91 Stockholm, Sweden
  4. Institut für Molekularbiologie, Universität Witten/Herdecke, D-58448 Witten, Germany

Correspondence to:

Joen Luirink, E-mail: luirink@bio.vu.nl

Received 16 January 1998; Accepted 27 February 1998; Revised 19 February 1998

Two distinct protein targeting pathways can direct proteins to the Escherichia coli inner membrane. The Sec pathway involves the cytosolic chaperone SecB that binds to the mature region of pre-proteins. SecB targets the pre-protein to SecA that mediates pre-protein translocation through the SecYEG translocon. The SRP pathway is probably used primarily for the targeting and assembly of inner membrane proteins. It involves the signal recognition particle (SRP) that interacts with the hydrophobic targeting signal of nascent proteins. By using a protein cross-linking approach, we demonstrate here that the SRP pathway delivers nascent inner membrane proteins at the membrane. The SRP receptor FtsY, GTP and inner membranes are required for release of the nascent proteins from the SRP. Upon release of the SRP at the membrane, the targeted nascent proteins insert into a translocon that contains at least SecA, SecY and SecG. Hence, as appears to be the case for several other translocation systems, multiple targeting mechanisms deliver a variety of precursor proteins to a common membrane translocation complex of the E.coli inner membrane.

  • Keywords:

    • protein targeting,
    • SecA,
    • SecY,
    • signal recognition particle,
    • translocon