Three-dimensional structure of O-acetylserine sulfhydrylase from Salmonella typhimurium.
The last step in cysteine biosynthesis in enteric bacteria is catalyzed by the pyridoxal 5'-phosphate-dependent enzyme O-acetylserine sulfhydrylase. Here we report the crystal structure at 2.2 A resolution of the A-isozyme of O-acetylserine sulfhydrylase isolated from Salmonella typhimurium. O-acetylserine sulfhydrylase shares the same fold with tryptophan synthase-beta from Salmonella typhimurium but the sequence identity level is below 20%. There are some major structural differences: the loops providing the interface to the alpha-subunit in tryptophan synthase-beta and two surface helices of tryptophan synthase-beta are missing in O-acetylserine sulfhydrylase. The hydrophobic channel for indole transport from the alpha to the beta active site of tryptophan synthase-beta is, not unexpectedly, also absent in O-acetylserine sulfhydrylase. The dimer interface, on the other hand, is more or less conserved in the two enzymes. The active site cleft of O-acetylserine sulfhydrylase is wider and therefore more exposed to the solvent. A possible binding site for the substrate O-acetylserine is discussed.
Department of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse70, Basel, CH-4056, Switzerland.
P
P
Burkhard
G S
GS
Rao
E
E
Hohenester
K D
KD
Schnackerz
P F
PF
Cook
J N
JN
Jansonius
D001665:Binding Sites; D018360:Crystallography, X-Ray; D003547:Cysteine Synthase / Q000737:chemistry*; D019281:Dimerization; D007211:Indoles; D008958:Models, Molecular; D011487:Protein Conformation; D011732:Pyridoxal Phosphate / Q000737:chemistry; D012486:Salmonella typhimurium / Q000201:enzymology*; D014367:Tryptophan Synthase / Q000737:chemistry
D007211:Indoles; D011732:Pyridoxal Phosphate; D003547:Cysteine Synthase; D014367:Tryptophan Synthase