Transfers a succinyl group from succinyl-CoA to L-serine, forming succinyl-L-serine. L-serine + succinyl-CoA = CoA + O-succinyl-L-serine Amino-acid biosynthesis; L-cysteine biosynthesis; L-cysteine from L-serine: step 1/2. Homodimer. Belongs to the AB hydrolase superfamily. MetX family.