Interaction of serine acetyltransferase with O-acetylserine sulfhydrylase active site: evidence from fluorescence spectroscopy.
Serine acetyltransferase is a key enzyme in the sulfur assimilation pathway of bacteria and plants, and is known to form a bienzyme complex with O-acetylserine sulfhydrylase, the last enzyme in the cysteine biosynthetic pathway. The biological function of the complex and the mechanism of reciprocal regulation of the constituent enzymes are still poorly understood. In this work the effect of complex formation on the O-acetylserine sulfhydrylase active site has been investigated exploiting the fluorescence properties of pyridoxal 5'-phosphate, which are sensitive to the cofactor microenvironment and to conformational changes within the protein matrix. The results indicate that both serine acetyltransferase and its C-terminal decapeptide bind to the alpha-carboxyl subsite of O-acetylserine sulfhydrylase, triggering a transition from an open to a closed conformation. This finding suggests that serine acetyltransferase can inhibit O-acetylserine sulfhydrylase catalytic activity with a double mechanism, the competition with O-acetylserine for binding to the enzyme active site and the stabilization of a closed conformation that is less accessible to the natural substrate.
Department of Biochemistry and Molecular Biology, Univeristy of Parma, 43100 Parma, Italy.
Barbara
B
Campanini
Francesca
F
Speroni
Enea
E
Salsi
Paul F
PF
Cook
Steven L
SL
Roderick
Bin
B
Huang
Stefano
S
Bettati
Andrea
A
Mozzarelli
D000123:Acetyltransferases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology; D001665:Binding Sites; D003545:Cysteine / Q000096:biosynthesis; D003547:Cysteine Synthase / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D011732:Pyridoxal Phosphate / Q000737:chemistry; D051050:Serine O-Acetyltransferase; D013050:Spectrometry, Fluorescence
D011732:Pyridoxal Phosphate; D000123:Acetyltransferases; D051050:Serine O-Acetyltransferase; D003547:Cysteine Synthase; D003545:Cysteine