Tat-dependent protein targeting in prokaryotes and chloroplasts.
The twin-arginine translocation (Tat) system operates in the chloroplast thylakoid and the plasma membranes of a wide range of bacteria. It recognizes substrates bearing cleavable signal peptides in which a twin-arginine motif almost invariably plays a key role in recognition by the translocation machinery. These signal peptides are surprisingly similar to those used to specify transport by Sec-type systems, but the Tat pathway differs in fundamental respects from Sec-type and other protein translocases. Its key attribute is its ability to translocate large, fully folded (even oligomeric) proteins across tightly sealed membranes. To date, three key tat genes have been characterised and the first details of the Tat system are beginning to emerge. In this article we review the salient features of Tat systems, with an emphasis on the targeting signals involved, the substrate specificities of Tat systems, our current knowledge of Tat complex structures and the known mechanistic features. Although the article is focused primarily on bacterial systems, we incorporate relevant aspects of plant thylakoid Tat work and we discuss how the plant and bacterial systems may differ in some respects.
Robinson
Colin
C
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK. Crobinson@bio.warwick.ac.uk <Crobinson@bio.warwick.ac.uk>
Bolhuis
Albert
A
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002736:Chloroplasts / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011487:Protein Conformation; D017510:Protein Folding; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology; D021381:Protein Transport / Q000502:physiology
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; C408585:twin-arginine translocase complex, E coli