Specifically catalyzes the decarboxylation of meso-diaminopimelate (meso-DAP) to L-lysine (By similarity). Plays a role in beta-lactam antibiotic resistance. H(+) + meso-2,6-diaminoheptanedioate = CO2 + L-lysine Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; L-lysine from DL-2,6-diaminopimelate: step 1/1. Homodimer. Disruption of this gene does not affect growth in rich organic media but reduces the level of methicillin resistance by nearly 100-fold. Belongs to the Orn/Lys/Arg decarboxylase class-II family. LysA subfamily.