Generates 3->3 cross-links in peptidoglycan, catalyzing the cleavage of the mDap(3)-D-Ala(4) bond of a tetrapeptide donor stem and the formation of a bond between the carbonyl of mDap(3) of the donor stem and the side chain of mDap(3) of the acceptor stem. Is specific for donor substrates containing a stem tetrapeptide since it cannot use pentapeptide stems. Is irreversibly inactivated by the beta-lactams carbapenems via the formation of a covalent adduct resulting from acylation of the catalytic Cys; imipenem is the most efficient drug for in vitro LdtMt2 inactivation. Cell wall biogenesis; peptidoglycan biosynthesis. Consists of two tandem immunoglobulin-like Big_5 domains in the N-terminal region (residues 56-145 and 150-250), followed by a L,D-transpeptidase catalytic domain (residues 251-378) and a C-terminal tail (residues 379-408). The peptidoglycan structure of stationary-phase M.tuberculosis is atypical since it contains a majority (80%) of 3->3 cross-links synthesized by L,D-transpeptidases that predominate over the 4->3 cross-links formed by the D,D-transpeptidase activity of classical penicillin-binding proteins (PubMed:18408028). In fact, 3-3 cross-linkages predominate throughout all growth phases and the ratio of 4-3/3-3 linkages does not vary significantly under any growth condition (PubMed:22906310).