Substrate specificity in thiamin diphosphate-dependent decarboxylases

Thiamin diphosphate (ThDP) is the biologically active form of vitamin B-1, and ThDP-dependent enzymes are found in all forms of life. The catalytic mechanism of this family requires the formation of a common intermediate, the 2 alpha-carbanion-enamine, regardless of whether the enzyme is involved in C-C bond formation or breakdown, or even formation of C-N, C-O and C-S bonds. This demands that the enzymes must screen substrates prior to, and/or after, formation of the common intermediate. This review is focused on the group for which the second step is the protonation of the 2 alpha-carbanion, i.e., the ThDP-dependent decarboxylases. Based on kinetic data, sequence/structure alignments and mutagenesis studies the factors involved in substrate specificity have been identified. (C) 2011 Elsevier Inc. All rights reserved.