Structure and function of the hetero-oligomeric cysteine synthase complex in plants.
Cysteine synthesis in bacteria and plants is catalyzed by serine acetyltransferase (SAT) and O-acetylserine (thiol)-lyase (OAS-TL), which form the hetero-oligomeric cysteine synthase complex (CSC). In plants, but not in bacteria, the CSC is assumed to control cellular sulfur homeostasis by reversible association of the subunits. Application of size exclusion chromatography, analytical ultracentrifugation, and isothermal titration calorimetry revealed a hexameric structure of mitochondrial SAT from Arabidopsis thaliana (AtSATm) and a 2:1 ratio of the OAS-TL dimer to the SAT hexamer in the CSC. Comparable results were obtained for the composition of the cytosolic SAT from A. thaliana (AtSATc) and the cytosolic SAT from Glycine max (Glyma16g03080, GmSATc) and their corresponding CSCs. The hexameric SAT structure is also supported by the calculated binding energies between SAT trimers. The interaction sites of dimers of AtSATm trimers are identified using peptide arrays. A negative Gibbs free energy (ΔG = -33 kcal mol(-1)) explains the spontaneous formation of the AtCSCs, whereas the measured SAT:OAS-TL affinity (K(D) = 30 nm) is 10 times weaker than that of bacterial CSCs. Free SAT from bacteria is >100-fold more sensitive to feedback inhibition by cysteine than AtSATm/c. The sensitivity of plant SATs to cysteine is further decreased by CSC formation, whereas the feedback inhibition of bacterial SAT by cysteine is not affected by CSC formation. The data demonstrate highly similar quaternary structures of the CSCs from bacteria and plants but emphasize differences with respect to the affinity of CSC formation (K(D)) and the regulation of cysteine sensitivity of SAT within the CSC.
Wirtz
Markus
M
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Birke
Hannah
H
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Heeg
Corinna
C
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Müller
Christopher
C
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Hosp
Fabian
F
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Throm
Christian
C
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
König
Stephan
S
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg.
Feldman-Salit
Anna
A
Heidelberg Institute for Theoretical Studies, 69118 Heidelberg.
Rippe
Karsten
K
BioQuant, University of Heidelberg, 69120 Heidelberg.
Petersen
Gabriele
G
Institute of Zoology, University of Heidelberg, 69120 Heidelberg.
Wade
Rebecca C
RC
Heidelberg Institute for Theoretical Studies, 69118 Heidelberg.
Rybin
Vladimir
V
EMBL Heidelberg, 69117 Heidelberg, Germany.
Scheffzek
Klaus
K
EMBL Heidelberg, 69117 Heidelberg, Germany.
Hell
Rüdiger
R
From the Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg. Electronic address: rhell@hip.uni-heidelberg.de.
D017360:Arabidopsis / Q000201:enzymology*; D001419:Bacteria / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D003547:Cysteine Synthase / Q000737:chemistry* / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology*; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D013025:Glycine max / Q000201:enzymology
D001426:Bacterial Proteins; D010940:Plant Proteins; D003547:Cysteine Synthase; D003545:Cysteine