The Tat protein export pathway and its role in cyanobacterial metalloprotein biosynthesis

The Tat pathway is a common protein translocation system that is found in the bacterial cytoplasmic membrane, as well as in the cyanobacterial and plant thylakoid membranes. It is unusual in that the Tat pathway transports fully folded, often metal cofactor-containing proteins across these membranes. In bacteria, the Tat pathway plays an important role in the biosynthesis of noncytoplasmic metalloproteins. By compartmentalizing protein folding to the cytoplasm, the potentially aberrant binding of non-native metal ions to periplasmic proteins is avoided. To date, most of our understanding of Tat function has been obtained from studies using Escherichia coli as a model organism but cyanobacteria have an extra layer of complexity with proteins targeted to both the cytoplasmic and thylakoid membranes. We examine our current understanding of the Tat pathway in cyanobacteria and its role in metalloprotein biosynthesis.