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primary topic: Assembly of the cysteine synthase complex and the regulatory role of protein-protein interactions.

Assembly of the cysteine synthase complex and the regulatory role of protein-protein interactions.
type: AcademicArticle
type: Article
abstract: Macromolecular assemblies play critical roles in regulating cellular functions. The cysteine synthase complex (CSC), which is formed by association of serine O-acetyltransferase (SAT) and O-acetylserine sulfhydrylase (OASS), acts as a sensor and modulator of thiol metabolism by responding to changes in nutrient conditions. Here we examine the oligomerization and energetics of formation of the soybean CSC. Biophysical examination of the CSC by size exclusion chromatography and sedimentation ultracentrifugation indicates that this assembly (complex M(r) approximately 330,000) consists of a single SAT trimer (trimer M(r) approximately 110,000) and three OASS dimers (dimer M(r) approximately 70,000). Analysis of the SAT-OASS interaction by isothermal titration calorimetry reveals negative cooperativity with three distinct binding events during CSC formation with K(d) values of 0.3, 7.5, and 78 nm. The three binding events are also observed using surface plasmon resonance with comparable affinities. The stability of the CSC derives from rapid association and extremely slow dissociation of OASS with SAT and requires the C terminus of SAT for the interaction. Steady-state kinetic analysis shows that CSC formation enhances SAT activity and releases SAT from substrate inhibition and feedback inhibition by cysteine, the final product of the biosynthesis pathway. Cysteine inhibits SAT and the CSC with K(i) values of 2 and 70 microm, respectively. These results suggest a new model for the architecture of this regulatory complex and additional control mechanisms for biochemically controlling plant cysteine biosynthesis. Based on previous work and our results, we suggest that OASS acts as an enzyme chaperone of SAT in the CSC.
date: 2009-04-10
volume: 284
issue: 15
is part of: The Journal of biological chemistry
status: peerReviewed
status: published
author list: authors
type: EPrint
type: ArticleEPrint
is part of: repository
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subject: QD Chemistry

Assembly of the cysteine synthase complex and the regulatory role of protein-protein interactions. (PDF)
type: Document
has file: kumaran2009.pdf
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ASBMB
type: Organization

The Journal of biological chemistry
type: Collection
issn: 00219258

Joseph M Jez
type: Person
given name: Joseph M
family name: Jez

Hankuil Yi
type: Person
given name: Hankuil
family name: Yi

Hari B Krishnan
type: Person
given name: Hari B
family name: Krishnan

Sangaralingam Kumaran
type: Person
given name: Sangaralingam
family name: Kumaran

Assembly of the cysteine synthase complex and the regulatory role of protein-protein interactions. (Indexer Terms)
type: Document
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primary topic: Assembly of the cysteine synthase complex and the regulatory role of protein-protein interactions.

QD Chemistry
type: Concept