The C-terminal domain (IV) is an [alpha]-helical domain formed by 19 [alpha]-helices that are organized into a superhelix
. The helices are: H12 (Ser582-Val589), H13 (Ser596-Ser612), H14 (Ser617-Arg628), H15 (Asn633-Thr647), H16 (Phe655-Ala668), H17 (Trp674-Phe689), H18 (Leu693-Asn702), H19 (Ser713-lle723), H20 (Ala727-Cys735), H21 (Leu740-Lys747), H22 (Leu757-Tyr762), H23 (Leu766), H24 (Leu777-Asn782), H25 (Ala787-Ala798), H26 (Asp802-Leu806), H27 (Ser813-Met814), H28 (Lys818-Phe828), H29 (Leu832-Glu837) and H30 (Va1842-Va1867).
Presently new STE morphologies are being generated with by use of advanced fabrication knowledge, as can be seen in Figure 4(b) with the creation of a double helix column, termed a superhelix
(Sunal 1999; Messier et al.