Multiple precursor proteins bind individual Tat receptor complexes and are collectively transported.

Area of Science:

• Cellular biology
• Protein transport mechanisms
• Plant molecular biology

Background:

• The thylakoid twin arginine protein translocation (Tat) system facilitates protein transport across membranes.
• Current models propose a multivalent receptor complex where each cpTatC-Hcf106 pair binds a single signal peptide.
• Translocation is thought to involve the assembly of a Tha4 oligomer with a single precursor-occupied receptor.

Purpose of the Study:

• To investigate the translocation capacity of the thylakoid Tat system beyond single precursor proteins.
• To determine if multiple precursor proteins can be transported concurrently by a single receptor complex.
• To elucidate the mechanism of oligomeric precursor protein translocation.

Main Methods:

• Utilizing precursor proteins with cysteine residues to induce disulfide bond formation and oligomerization.
• Employing Blue native-polyacrylamide gel electrophoresis (BN-PAGE) to analyze oligomer association with receptor complexes.
• Assessing the transport efficiency of monomeric versus oligomeric precursors across the membrane.

Main Results:

• Multiple precursor proteins bound to a single receptor complex were observed to be transported together.
• Precursor proteins readily formed dimeric and tetrameric forms via intermolecular disulfide bonds upon receptor binding.
• BN-PAGE confirmed that these oligomers were bound to individual receptor complexes, not bridging multiple complexes.
• Oligomeric precursors exhibited translocation efficiencies comparable to monomeric precursors.

Conclusions:

• The thylakoid Tat system exhibits a novel mechanism allowing the simultaneous transport of multiple, interlinked precursor proteins.
• A single receptor complex can accommodate and transport oligomeric precursor proteins.
• This finding expands our understanding of the flexibility and capacity of the Tat protein translocation machinery.