Catalyzes the attachment of threonine to tRNA(Thr) in a two-step reaction: L-threonine is first activated by ATP to form Thr-AMP and then transferred to the acceptor end of tRNA(Thr) (Probable). This protein is probably not able to deacylate mischarged L-seryl-tRNA(Thr) as it lacks the appropriate domain (PubMed:19761773). ATP + L-threonine + tRNA(Thr) = AMP + diphosphate + H(+) + L-threonyl-tRNA(Thr) Binds 1 zinc ion per subunit. Homodimer (PubMed:19761773). Probably interacts with its editing subunit (By similarity). There are two ThrRS in this archaeon. The first one (APE_0809.1, this entry) is most similar to bacterial ThrRS but it lacks the N-terminal editing domain. The second one (APE_0117.1, AC Q9YFY3) is most similar to archaeal ThrRS but lacks the central catalytic domain; it probably does not aminoacylate tRNA(Thr). Belongs to the class-II aminoacyl-tRNA synthetase family.