Catalyzes the ATP-dependent 2-thiolation of cytidine in position 32 of tRNA, to form 2-thiocytidine (s(2)C32). The sulfur atoms are provided by the cysteine/cysteine desulfurase (IscS) system. AH2 + ATP + cytidine(32) in tRNA + S-sulfanyl-L-cysteinyl-[cysteine desulfurase] = 2-thiocytidine(32) in tRNA + A + AMP + diphosphate + H(+) + L-cysteinyl-[cysteine desulfurase] Binds 1 [4Fe-4S] cluster per subunit. The cluster is chelated by three Cys residues, the fourth Fe has a free coordination site that may bind a sulfur atom transferred from the persulfide of IscS. tRNA modification. Homodimer. Present in outer membrane vesicle formulations which are used as vaccines in human. The thiolation reaction likely consists of two steps: a first activation step by ATP to form an adenylated intermediate of the target base of tRNA, and a second nucleophilic substitution step of the sulfur (S) atom supplied by the hydrosulfide attached to the Fe-S cluster. Belongs to the TtcA family.