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Serine acetyltransferase (SAT): SAT catalyzes the CoA-dependent acetylation of the side chain hydroxyl group of L-serine to form O-acetylserine, as the first step of a two-step biosynthetic pathway in bacteria and plants leading to the formation of L-cysteine. This reaction represents a key metabolic point of regulation for the cysteine biosynthetic pathway due to its feedback inhibition by cysteine. The enzyme is a 175 kDa homohexamer, composed of a dimer of homotrimers. Each subunit contains an N-terminal alpha helical region and a C-terminal left-handed beta-helix (LbH) subdomain with 5 turns, each containing a hexapeptide repeat motif characteristic of the acyltransferase superfamily of enzymes. The trimer interface mainly involves the C-terminal LbH subdomain while the dimer (of trimers) interface is mediated by the N-terminal alpha helical subdomain.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",