Interconvertibility of lipid- and translocon-bound forms of the bacterial Tat precursor pre-SufI.
Signal peptides target protein cargos for secretion from the bacterial cytoplasm. These signal peptides contain a tri-partite structure consisting of a central hydrophobic domain (h-domain), and two flanking polar domains. Using a recently developed in vitro transport assay, we report here that a central h-domain position (C17) of the twin arginine translocation (Tat) substrate pre-SufI is especially sensitive to amino acid hydrophobicity. The C17I mutant is transported more efficiently than wild type, whereas charged substitutions completely block transport. Transport efficiency is well-correlated with Tat translocon binding efficiency. The precursor protein also binds to non-Tat components of the membrane, presumably to the lipids. This lipid-bound precursor can be chased through the Tat translocons under conditions of high proton motive force. Thus, the non-Tat bound form of the precursor is a functional intermediate in the transport cycle. This intermediate appears to directly equilibrate with the translocon-bound form of the precursor.
Bageshwar
Umesh K
UK
Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843, USA.
Whitaker
Neal
N
Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843, USA.
Liang
Fu-Cheng
FC
Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843, USA.
Musser
Siegfried M
SM
Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843, USA.
D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D021382:Protein Sorting Signals; D021381:Protein Transport
D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; C473632:SufI protein, E coli