This is domain (D-VI) can be found in Bacillus thuringiensis (Bt) insecticidal protein Cry1Ac. Full length structural analysis reveal that Cry1Ac contains seven distinct domains (DI-DVII): the three canonical toxin core domains (D-I through D-III) and four protoxin domains (D-IV through D-VII). Cry1Ac is sickle-shaped with the toxic core as handle and the protoxin domains as the blade. Domains IV and VI are alpha-bundles that resemble structural/interaction domains such as spectrin [PDB ID: 1CUN] or bacterial fibrinogen-binding complement inhibitor [1].

1: Structure of the full-length insecticidal protein Cry1Ac reveals intriguing details of toxin packaging into in vivo formed crystals. Evdokimov AG, Moshiri F, Sturman EJ, Rydel TJ, Zheng M, Seale JW, Franklin S; Protein Sci. 2014;23:1491-1497. PMID:25139047