Required for the formation of a threonylcarbamoyl group on adenosine at position 37 (t(6)A37) in tRNAs that read codons beginning with adenine. Is involved in the transfer of the threonylcarbamoyl moiety of threonylcarbamoyl-AMP (TC-AMP) to the N6 group of A37, together with TsaE and TsaB. TsaD likely plays a direct catalytic role in this reaction (By similarity). Critical mediator involved in the modification of cell wall peptidoglycan synthesis and/or cell division as well as in the positive regulation of the activities of different murein hydrolases. Essential for cell viability. Negatively affects the expression of lrgA. Positively affects cidA expression, maybe indirectly. May be an important chelator of excess zinc. Down-regulation of gcp/tsaD eliminates penicillin- and vancomycin-caused cell lysis, inhibits several extracellular hydrolase activities, dramatically increasing tolerance to hydrolases and leads to a bacteriostatic effect. adenosine(37) in tRNA + L-threonylcarbamoyladenylate = AMP + H(+) + N(6)-L-threonylcarbamoyladenosine(37) in tRNA Binds 1 Fe(2+) ion per subunit. Belongs to the KAE1 / TsaD family.