Journal of Biological Chemistry
Volume 287, Issue 33, 10 August 2012, Pages 27941-27947
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Plant Biology
Mitochondrial Cysteine Synthase Complex Regulates O-Acetylserine Biosynthesis in Plants*

https://doi.org/10.1074/jbc.M112.372656Get rights and content
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Cysteine synthesis is catalyzed by serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL) in the cytosol, plastids, and mitochondria of plants. Biochemical analyses of recombinant plant SAT and OAS-TL indicate that the reversible association of the proteins in the cysteine synthase complex (CSC) controls cellular sulfur homeostasis. However, the relevance of CSC formation in each compartment for flux control of cysteine synthesis remains controversial. Here, we demonstrate the interaction between mitochondrial SAT3 and OAS-TL C in planta by FRET and establish the role of the mitochondrial CSC in the regulation of cysteine synthesis. NMR spectroscopy of isolated mitochondria from WT, serat2;2, and oastl-C plants showed the SAT-dependent export of OAS. The presence of cysteine resulted in reduced OAS export in mitochondria of oastl-C mutants but not in WT mitochondria. This is in agreement with the stronger in vitro feedback inhibition of free SAT by cysteine compared with CSC-bound SAT and explains the high OAS export rate of WT mitochondria in the presence of cysteine. The predominant role of mitochondrial OAS synthesis was validated in planta by feeding [3H]serine to the WT and loss-of-function mutants for OAS-TLs in the cytosol, plastids, and mitochondria. On the basis of these results, we propose a new model in which the mitochondrial CSC acts as a sensor that regulates the level of SAT activity in response to sulfur supply and cysteine demand.

Amino Acid Transport
Plant Biochemistry
Plant Physiology
Protein-Protein Interactions
Serine
Cysteine
Cysteine Synthase Complex
O-Acetylserine
Serine Acetyltransferase

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*

This work was supported by the Landesgraduiertenförderung Baden-Württemberg (Hartmut Hoffmann-Berling International Graduate School of Molecular and Cellular Biology, BioQant Graduate School Molecular Machines), the Schmeil-Stiftung (Heidelberg), and Deutsche Forschungsgemeinschaft Grants He1848/5-2 and He1848/13-1) (to C. H.); a UK Biotechnology and Biological Sciences Research Council CASE studentship and Advanced Technologies (Cambridge, United Kingdom) (to K. F. M. B.); and a New College Oxford Weston junior research fellowship (to M. S.).

This article contains supplemental Figs. 1–3.

1

Both authors contributed equally to this work.

2

Present address: Inst. of Crop Science and Resource Conservation, University of Bonn, 53115 Bonn, Germany.