Specifically catalyzes the decarboxylation of meso-diaminopimelate (meso-DAP) to L-lysine. Is not active against the DD- or LL-isomers of diaminopimelate. H(+) + meso-2,6-diaminoheptanedioate = CO2 + L-lysine Is activated by 2,3-dimercaptopropan-1-ol. Optimum pH is 6.7-6.8. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; L-lysine from DL-2,6-diaminopimelate: step 1/1. Up-regulated by LysR. Repressed in the presence of lysine. Belongs to the Orn/Lys/Arg decarboxylase class-II family. LysA subfamily.