Download Identification of translocon subcomplexes associated with chloroplast

Title：Identification of translocon subcomplexes associated with chloroplast
protein import intermediates
M.S. student ： Kuan-Yu Chen (R92B42017)
Advisor：Dr. Hsou-Min Li
Abstract：
Most chloroplast proteins are encoded by the nucleus, synthesized in the cytosol
and imported into chloroplasts. These nucleus-encoded proteins are synthesized as
precursors with N-terminal transit peptides, and are transported into chloroplasts by a
set of translocon complex located in the chloroplast outer and inner envelope
membranes. Translocon components are termed Toc (translocons at the outer envelope
membrane of chloroplasts) and Tic (translocons at the inner envelope membrane of
chloroplasts) proteins. We use sucrose density gradient and BN-PAGE (Blue Native
Polyacrylamide Electrophoresis) to separate complexes that are intermediates in
importing preproteins. Here are our conclusions.
• We have identified two Toc complex intermediates, C1-1 and C1-2, and two
TicToc supercomplex intermediates,C2 and TicToc.
• C1-1 is a Toc subcomplex containing Toc75、Toc34 but not Toc159. Its
molecular mass is about 700 kDa.
• C1-2 is a complete Toc complex containing Toc75、Toc34 & Toc159. Its
molecular mass is about 700 kDa also.
• C2 is a TicToc subcomplex containing Toc75、Toc34、Toc159 & Tic110. Its
molecular mass is about 800 kDa.
• TicToc is a supercomplex containing all of the Tic、Toc components. Its
molecular mass is at least more than 2 mDa.
• All of these complexes are functional intermediates in the chloroplast protein
import process.
• By importing other precursors, we found these four complexes are general
complexes for all precursors tested.
• We propose the chloroplast preprotein import pathway is C1
->C2->TicToc->stroma.