PMID:10766774
| Citation |
Stanley, NR, Palmer, T and Berks, BC (2000) The twin arginine consensus motif of Tat signal peptides is involved in Sec-independent protein targeting in Escherichia coli. J. Biol. Chem. 275:11591-6 |
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| Abstract |
In Escherichia coli a subset of periplasmic proteins is exported through the Tat pathway to which substrates are directed by an NH(2)-terminal signal peptide containing a consensus SRRXFLK "twin arginine" motif. The importance of the individual amino acids of the consensus motif for in vivo Tat transport has been assessed by site-directed mutagenesis of the signal peptide of the Tat substrate pre-SufI. Although the invariant arginine residues are crucial for efficient export, we find that slow transport of SufI is still possible if a single arginine is conservatively substituted by a lysine residue. Thus, in at least one signal peptide context there is no absolute dependence of Tat transport on the arginine pair. The consensus phenylalanine residue was found to be a critical determinant for efficient export but could be functionally substituted by leucine, another amino acid with a highly hydrophobic side chain. Unexpectedly, the consensus lysine residue was found to retard Tat transport. These observations and others suggest that the sequence conservation of the Tat consensus motif is a reflection of the functional importance of the consensus residues. Tat signal peptides characteristically have positively charged carboxyl-terminal regions. However, changing the sign of this charge does not affect export of SufI. |
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| Keywords |
Amino Acid Substitution; Arginine/analysis; Arginine/genetics; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Carrier Proteins/chemistry; Carrier Proteins/genetics; Consensus Sequence; Escherichia coli/metabolism; Escherichia coli Proteins; Lysine/analysis; Lysine/genetics; Membrane Transport Proteins; Mutagenesis, Site-Directed; Serine/analysis; Serine/genetics |
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