What is the Difference Between SEC and TAT Pathway

The key difference between SEC and TAT pathway is that the SEC pathway transport unfolded proteins while the TAT pathway transport folded proteins.

Protein synthesis and transport mechanisms are common in all animals, plants, archaea, and bacteria. Protein transport refers to the movement of proteins from cellular or extracellular compartments to another. SEC pathway and TAT pathway are two such systems involved in the transportation of proteins. These systems transport proteins either across the cytoplasmic membrane or the plasma membrane. The process of such transportation varies from organism to organism, depending on the advanced nature. SEC pathway is more advanced than the TAT pathway since it consists of different subcategories and more advanced signaling systems. Both systems’ transportation pathways are facilitated by endocytosis, exocytosis, protein translocation, and membrane trafficking.

CONTENTS

1. Overview and Key Difference
2. What is SEC Pathway
3. What is TAT Pathway
4. Similarities – SEC and TAT Pathway
5. SEC vs TAT Pathway in Tabular Form
6. Summary – SEC vs TAT Pathway

What is SEC Pathway?

SEC pathway or secretory pathway is a carrier pathway that comprises ubiquitous and universal export machinery for most proteins integrated into or translocated through the plasma membrane. This is an essential pathway in the biological systems which induces the transportation of proteins to the cell membrane, where they get released. For many proteins, the SEC pathway occurs at a relatively constant rate. The synthesizing rate of proteins directly affects the transportation rate. During the SEC pathway, the transportation of proteins takes place in an unfolded manner.

Proteins that are targeted to the SEC pathway are comprised of two groups. One group of proteins includes the proteins that function in the ER and Golgi to ensure proper protein folding and modification (resident proteins). The second group of proteins includes the proteins that are processed in ER and Golgi and transported to later compartments such as the plasma membrane, lysosomes, and extracellular space. These proteins possess two signaling mechanisms. One signal instructs the proteins to enter the secretory pathway, and the second signal instructs the proteins to localize it to a particular organelle within the pathway.

What is TAT Pathway?

TAT pathway or twin-arginine translocation pathway is a protein transportation pathway found in plants, bacteria, and archaea. During this pathway, proteins get transported in a folded manner across a lipid membrane bilayer. In plants, the TAT pathway is present in the thylakoid membrane of the chloroplast. Here, the proteins translocate into the thylakoid lumen. In bacteria, it is present in the cytoplasmic membrane and transports proteins to the cell envelope.

During the process of the TAT pathway, the folding of proteins takes place before transport since they contain redox cofactors that are inserted in the cytoplasm. Folding also helps to avoid the insertion of the incorrect metal ion cofactor at the active site. For bacteria and archaea, the requirement of the TAT pathway varies. In some organisms, it is an essential transport mechanism, while in others, it is non-essential. In some archaea and bacteria, the TAT pathway is completely absent. TAT pathway also depends on basic transport mechanisms such as membrane trafficking, protein translocation, and endocytosis or exocytosis.

What are the Similarities Between SEC and TAT Pathway?

• SEC and TAT pathways are essential components in the living system for transportation purposes.
• They are involved in the transportation of proteins.
• Moreover, both pathways function according to a particular signaling system.
• Both SEC and TAT pathways are facilitated by either membrane trafficking, protein translocation, and endocytosis or exocytosis.

What is the Difference Between SEC and TAT Pathway?

The key difference between SEC and TAT pathway is that the SEC pathway transports unfolded proteins while the TAT pathway transports folded proteins. SEC pathway is most common in animals. TAT pathway is most common in plants, archaea, and bacteria. Moreover, the SEC pathway is available in all animals and functions as an essential component. TAT pathway, on the other hand, could be essential, non-essential, or completely absent.

The below infographic presents the differences between SEC and TAT pathway in tabular form for side by side comparison.

Summary – SEC vs TAT Pathway

Protein synthesis and transport mechanisms are common in all animals, plants, archaea, and bacteria. Protein transport involves the movement of proteins from cellular or extracellular compartments to another. SEC pathway and TAT pathway are two such systems involved in the transportation of proteins. The key difference between SEC and TAT pathway is that the SEC pathway transports unfolded proteins while the TAT pathway transports folded proteins. Both systems’ transportation pathways are facilitated by endocytosis, exocytosis, protein translocation, and membrane trafficking.

Reference:

1. Palmer, Tracy, and Ben C. Berks. “The Twin-Arginine Translocation (TAT) Protein Export Pathway.” Nature News, Nature Publishing Group, 11 June 2012.
2. Tsirigotaki, Alexandra, et al. “Protein Export through the Bacterial SEC Pathway.” Nature News, Nature Publishing Group, 28 Nov. 2016.

Image Courtesy:

1. “Organelles of the Secretory Pathway” By Artwork by Holly Fischer – Cell Biology Slide 11; Histology of Glands Slide 4 (CC BY 3.0) via Commons Wikimedia
2. “Protein targeting to the thylakoid diagram” By BlueRidgeKitties (CC BY 2.0) via Flickr