This domain was first discovered in BPSL1050, a highly immunoreactive protein found in Burkholderia pseudomallei. The domain's structure consists of three helical regions which pack onto an antiparallel beta sheet, formed by four strands. The beta sheet is solvent exposed on one side and packs tightly against the three helices on the other side, generating a network of hydrophobic and aromatic interactions that contribute to tight packing of the protein. Is is thought that the small loop L1, the main loop L2, and part of helix alpha-3 extending until Leu120 are the three main immunogenic sequences [1].

1: Structure-based design of a B cell antigen from B. pseudomallei. Gaudesi D, Peri C, Quilici G, Gori A, Ferrer-Navarro M, Conchillo-Sole O, Thomas R, Nithichanon A, Lertmemongkolchai G, Titball R, Daura X, Colombo G, Musco G; ACS Chem Biol. 2015;10:803-812. PMID:25495888