Protein D-63 from Sulfolobus spindle-shape virus 1 (SSV1) folds into a helix-turn-helix motif with the two helices running antiparallel to each other. It adopts a dimeric assembly and forms an antiparallel four-helix bundle. It might be involved in macromolecular assembly as an adaptor protein [1].

1: Structure of D-63 from sulfolobus spindle-shaped virus 1: surface properties of the dimeric four-helix bundle suggest an adaptor protein function. Kraft P, Kummel D, Oeckinghaus A, Gauss GH, Wiedenheft B, Young M, Lawrence CM; J Virol. 2004;78:7438-7442. PMID:15220417