9.B.364. The Putative ArabinosylTransferase B (AraTB) Family
These proteins are large (~1100 aas with about 12 - 15 TMSs. 9.B.364.1.1 has 1083 aas and 13 putative TMSs in a 1 (N-terminus) + 12 TMS arrangement followed by a hydrophilic domain. This may be the general topology for the members of this family. The arabinosyltransferases EmbA, EmbB, and EmbC (TC# 9.B.364.1.5) are involved in Mycobacterium tuberculosis cell wall synthesis and are recognized as targets for the anti-tuberculosis drug ethambutol. Zhang et al. 2020 determined cryo-EM and x-ray crystal structures of the mycobacterial EmbA-EmbB and EmbC-EmbC complexes in the presence of their glycosyl donor and acceptor substrates and with ethambutol. These structures show how the donor and acceptor substrates bind in the active site and how ethambutol inhibits arabinosyltransferases by binding to the same site as both substrates in EmbB and EmbC. Most drug-resistant mutations are located near the ethambutol binding site.