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Protein Transport to the Thylakoids

Protein Transport to the Thylakoids

Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...

Protein Transport to the Stroma

Protein Transport to the Stroma

Chloroplasts are triple membrane structures with an outer membrane, an inner membrane, and a thylakoid membrane, each containing distinct metabolite transporters, membrane translocons, and enzymes. Appropriate sorting and translocating these proteins to their correct membrane systems is essential for chloroplast function.
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...

Protein Transport to the Inner Chloroplast Membrane

Protein Transport to the Inner Chloroplast Membrane

Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...

Protein Transport to the Outer Chloroplast Membrane

Protein Transport to the Outer Chloroplast Membrane

Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.

The ADP/ATP Carrier Protein

The ADP/ATP Carrier Protein

ADP/ATP carrier or AAC protein is the most abundant carrier protein in the inner mitochondrial membrane. It transports large quantities of ADP and ATP, equivalent to the average human body weight, every day. Among other transporters, ACC protein is one of the best-studied members of the mitochondrial carrier protein family. The ADP/ATP carrier protein comprises two transmembrane helices connected to a loop and a single alpha-helix on the matrix side. It switches between two conformational...

Translocation of Proteins into the Mitochondria

Translocation of Proteins into the Mitochondria

Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...

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Related Experiment Video

Updated: Jul 2, 2026

2 in 1: One-step Affinity Purification for the Parallel Analysis of Protein-Protein and Protein-Metabolite Complexes

2 in 1: One-step Affinity Purification for the Parallel Analysis of Protein-Protein and Protein-Metabolite Complexes

Published on: August 6, 2018

AtPTR1 and AtPTR5 transport dipeptides in planta.

Nataliya Y Komarova¹, Kathrin Thor, Adrian Gubler

¹Molecular Plant Physiology, Institute of Plant Sciences, University of Bern, Bern, Switzerland.

Plant Physiology

|August 30, 2008

Summary

Plant peptide transporters (PTR/NRT1 family) have distinct roles. AtPTR5 transports peptides in pollen and seeds, while AtPTR1 aids root nitrogen uptake, highlighting dipeptides as a key plant nutrient source.

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Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays

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Last Updated: Jul 2, 2026

2 in 1: One-step Affinity Purification for the Parallel Analysis of Protein-Protein and Protein-Metabolite Complexes

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Published on: August 6, 2018

Peptide-derived Method to Transport Genes and Proteins Across Cellular and Organellar Barriers in Plants

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Published on: December 16, 2016

Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays

Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays

Published on: September 28, 2018

Area of Science:

Plant molecular biology
Plant physiology
Biochemistry

Background:

Peptide transporters are crucial for nutrient uptake in plants.
The PTR/NRT1 family is large and its members' functions are not fully understood.
Understanding specific transporter roles is key to plant nutrition.

Purpose of the Study:

To characterize a novel peptide transporter, AtPTR5, from Arabidopsis thaliana.
To compare the in planta functions of AtPTR5 and the related AtPTR1.
To investigate the role of dipeptides as a nitrogen source for plants.

Main Methods:

Gene isolation and expression analysis of AtPTR5.
Creation and analysis of mutant and overexpressing Arabidopsis lines (atptr5, atptr1, double mutants, AtPTR5-overexpressing).
Phenotypic analysis of plant growth, pollen germination, and nitrogen content under dipeptide exposure, including toxic peptides.

Main Results:

AtPTR5 facilitates dipeptide transport into pollen, ovules, and seeds.
AtPTR1 is primarily involved in peptide uptake by roots, impacting nitrogen levels and growth.
Overexpression of AtPTR5 enhanced shoot growth and nitrogen content.

Conclusions:

Closely related PTR/NRT1 family members exhibit specialized functions in plants.
Dipeptides serve as a significant nitrogen source and transport form in plants, beyond amino acids.
AtPTR5 and AtPTR1 play distinct, vital roles in plant development and nutrient acquisition.