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Functional analysis of the cysteine synthase protein complex from plants: structural, biochemical and regulatory properties.
J Plant Physiol 2006; 163(3):273-86JP

Abstract

Cysteine synthesis in plants represents the final step of assimilatory sulfate reduction and the almost exclusive entry reaction of reduced sulfur into metabolism not only of plants, but also the human food chain in general. It is accomplished by the sequential reaction of two enzymes, serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL). Together they form the hetero-oligomeric cysteine synthase complex (CSC). Recent evidence is reviewed that identifies the dual function of the CSC as a sensor and as part of a regulatory circuit that controls cellular sulfur homeostasis. Computational modeling of three-dimensional structures of plant SAT and OAS-TL based on the crystal structure of the corresponding bacterial enzymes supports quaternary conformations of SAT as a dimer of trimers and OAS-TL as a homodimer. These findings suggest an overall alpha6beta4 structure of the subunits of the plant CSC. Kinetic measurements of CSC dissociation triggered by the reaction intermediate O-acetylserine as well as CSC stabilization by sulfide indicate quantitative reactions that are suited to fine-tune the equilibrium between free and associated CSC subunits. In addition, in vitro data show that SAT requires binding to OAS-TL for full activity, while at the same time bound OAS-TL becomes inactivated. Since OAS concentrations inside cells increase upon sulfate deficiency, whereas sulfide concentrations most likely decrease, these data suggest the dissociation of the CSC in vivo, accompanied by inactivation of SAT and activation of OAS-TL function in their free homo-oligomer states. Biochemical evidence describes this protein-interaction based mechanism as reversible, thus closing the regulatory circuit. The properties of the CSC and its subunits are therefore consistent with models of positive regulation of sulfate uptake and reduction in plants by OAS as well as a demand-driven repression/de-repression by a sulfur intermediate, such as sulfide.

Authors+Show Affiliations

Heidelberg Institute of Plant Sciences (HIP), University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg, Germany.No affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Review

Language

eng

PubMed ID

16386330

Citation

Wirtz, Markus, and Rüdiger Hell. "Functional Analysis of the Cysteine Synthase Protein Complex From Plants: Structural, Biochemical and Regulatory Properties." Journal of Plant Physiology, vol. 163, no. 3, 2006, pp. 273-86.
Wirtz M, Hell R. Functional analysis of the cysteine synthase protein complex from plants: structural, biochemical and regulatory properties. J Plant Physiol. 2006;163(3):273-86.
Wirtz, M., & Hell, R. (2006). Functional analysis of the cysteine synthase protein complex from plants: structural, biochemical and regulatory properties. Journal of Plant Physiology, 163(3), pp. 273-86.
Wirtz M, Hell R. Functional Analysis of the Cysteine Synthase Protein Complex From Plants: Structural, Biochemical and Regulatory Properties. J Plant Physiol. 2006;163(3):273-86. PubMed PMID: 16386330.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Functional analysis of the cysteine synthase protein complex from plants: structural, biochemical and regulatory properties. AU - Wirtz,Markus, AU - Hell,Rüdiger, Y1 - 2005/12/28/ PY - 2005/09/01/received PY - 2005/11/29/revised PY - 2005/11/30/accepted PY - 2006/1/3/pubmed PY - 2006/3/28/medline PY - 2006/1/3/entrez SP - 273 EP - 86 JF - Journal of plant physiology JO - J. Plant Physiol. VL - 163 IS - 3 N2 - Cysteine synthesis in plants represents the final step of assimilatory sulfate reduction and the almost exclusive entry reaction of reduced sulfur into metabolism not only of plants, but also the human food chain in general. It is accomplished by the sequential reaction of two enzymes, serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL). Together they form the hetero-oligomeric cysteine synthase complex (CSC). Recent evidence is reviewed that identifies the dual function of the CSC as a sensor and as part of a regulatory circuit that controls cellular sulfur homeostasis. Computational modeling of three-dimensional structures of plant SAT and OAS-TL based on the crystal structure of the corresponding bacterial enzymes supports quaternary conformations of SAT as a dimer of trimers and OAS-TL as a homodimer. These findings suggest an overall alpha6beta4 structure of the subunits of the plant CSC. Kinetic measurements of CSC dissociation triggered by the reaction intermediate O-acetylserine as well as CSC stabilization by sulfide indicate quantitative reactions that are suited to fine-tune the equilibrium between free and associated CSC subunits. In addition, in vitro data show that SAT requires binding to OAS-TL for full activity, while at the same time bound OAS-TL becomes inactivated. Since OAS concentrations inside cells increase upon sulfate deficiency, whereas sulfide concentrations most likely decrease, these data suggest the dissociation of the CSC in vivo, accompanied by inactivation of SAT and activation of OAS-TL function in their free homo-oligomer states. Biochemical evidence describes this protein-interaction based mechanism as reversible, thus closing the regulatory circuit. The properties of the CSC and its subunits are therefore consistent with models of positive regulation of sulfate uptake and reduction in plants by OAS as well as a demand-driven repression/de-repression by a sulfur intermediate, such as sulfide. SN - 0176-1617 UR - https://www.unboundmedicine.com/medline/citation/16386330/Functional_analysis_of_the_cysteine_synthase_protein_complex_from_plants:_structural_biochemical_and_regulatory_properties_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0176-1617(05)00461-X DB - PRIME DP - Unbound Medicine ER -