alpha-acetolactate decarboxylase (AldB, E.C. 4.1.1.5) converts acetolactate ((2S)-2-hydroxy-2-methyl-3-oxobutanoate) into acetoin ((3R)-3-hydroxybutan-2-one) and CO(2). Acetoin may be secreted by the cells, perhaps in order to control the internal pH. AldB may function as a regulator in valine and leucine biosynthesis and in catalyzing the second step of the 2,3-butanediol pathway. The structure of this domain displays an alpha-beta-beta-alpha four layer topology, with an HxHxxxxxxxxxxH motif (x could be any residue) that coordinates a zinc ion.
Jiyao W et al.(2023). "The conserved domain database in 2023.",