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Protein Transport to the Inner Chloroplast Membrane

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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...

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Related Experiment Video

Updated: Jun 7, 2026

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

Plastids contain a second sec translocase system with essential functions.

Courtney A Skalitzky¹, Jonathan R Martin, Jessica H Harwood

¹Department of Botany, University of Wisconsin, Madison, Wisconsin 53706-1381, USA.

Plant Physiology

|November 6, 2010

Summary

Researchers discovered two distinct Sec systems in plastids. One system, SCY1, is vital for thylakoid protein targeting, while the newly identified SCY2 system targets proteins to the inner envelope membrane.

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Last Updated: Jun 7, 2026

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

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Published on: September 28, 2018

Identification of Plasmodesmal Localization Sequences in Proteins In Planta

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Published on: August 15, 2017

Studying Protein Import into Chloroplasts Using Protoplasts

Studying Protein Import into Chloroplasts Using Protoplasts

Published on: December 10, 2018

Area of Science:

Plant Biology
Cell Biology
Molecular Biology

Background:

Proteins synthesized in the cytoplasm but functioning in plastids require import and precise targeting.
While thylakoid targeting systems are known, the mechanism for inner envelope membrane protein integration from the stroma remained undescribed.

Purpose of the Study:

To identify and characterize the systems responsible for targeting proteins to specific plastid locations, particularly the inner envelope membrane.
To elucidate the distinct functions of different Sec systems within plastids.

Main Methods:

Genetic analysis using loss-of-function mutations in Arabidopsis thaliana.
Localization studies including chloroplast import assays, fractionation, and immunogold labeling.
Promoter-swap experiments to assess functional redundancy.

Main Results:

Two distinct Sec systems (SCY1 and SCY2) with non-redundant functions were identified in plastids.
Mutations in the SCY1 system (SCY1, SECA1, SECE1) led to albino seedlings and altered growth.
Mutations in the SCY2 system (SCY2, SECA2) caused embryo lethality, and SCY2 was localized to the envelope membrane.

Conclusions:

SCY1 and its components are involved in thylakoid protein targeting.
SCY2 and SECA2 constitute a novel envelope-localized Sec system essential for inner envelope membrane protein integration and translocation.
This discovery reveals a new pathway for protein targeting within plastids.