Twin-arginine translocation pathway

Twin-arginine translocation pathway (Tat pathway) is a protein export system found in bacteria, archaea, and chloroplasts. It is distinct from other protein export pathways in that it transports fully folded proteins across the inner cell membrane. This pathway is named after the twin arginine residues found in the signal peptide of proteins targeted for export.

Overview

The Tat pathway is responsible for the translocation of proteins across the cell membrane or thylakoid membrane in chloroplasts. Unlike the Sec pathway, which translocates proteins in an unfolded state, the Tat pathway can transport proteins that have already achieved their native, folded conformation. This unique feature is crucial for the export of proteins that contain tightly bound cofactors or are otherwise sensitive to unfolding.

Components

The core components of the Tat pathway are the TatA, TatB, and TatC proteins. These proteins form a complex that spans the cell membrane and facilitates the transport of proteins.

• TatA - Forms the pore through which proteins are translocated. Its oligomerization is thought to be triggered by the binding of a substrate protein to the TatBC complex.
• TatB - Works in conjunction with TatC to recognize and bind substrate proteins. It plays a critical role in the initial stages of the translocation process.
• TatC - Serves as the receptor for the signal peptide of substrate proteins. It is involved in the assembly of the TatABC complex.

Mechanism

The translocation process begins with the recognition of the twin-arginine motif in the signal peptide of the substrate protein by the TatBC complex. Once bound, the substrate protein is delivered to the TatA component, leading to the assembly of a larger TatA complex. This complex forms a transient pore through which the substrate protein is translocated across the membrane. Remarkably, the process does not require the unfolding of the substrate protein, allowing the transport of fully folded proteins and those with bound cofactors.

Biological Significance

The Tat pathway plays a vital role in the physiology of bacteria and plants. In bacteria, it is involved in the export of enzymes necessary for processes such as nitrogen fixation and photosynthesis. In plants, the pathway is essential for the proper functioning of chloroplasts, as it is responsible for the import of proteins required for photosynthesis.

Clinical Implications

Understanding the Tat pathway has potential implications for the development of new antibiotics and the production of therapeutic proteins. Inhibitors of the Tat pathway could serve as novel antimicrobial agents, while the pathway's ability to transport folded proteins could be harnessed for the efficient production of complex therapeutic proteins.

See Also

• Protein targeting
• Signal peptide
• Sec (secretion) pathway
• Protein translocation