There are two different formats for the 6-helix bundle; one closes up to form a simple six-helix
bundle whose ends are opposite one another. This molecule is shown in Figure 1b. However,
the other one, shown in Figure 1c, is an overlapping structure, so that one BTX is phased half
the length away from the other, leading to an overlapping structure. In both cases, a half-helix
is designed to fit with another half-helix so that a tube can be formed. The differences can be
noted in the longitudinal views: Six differently colored helices are evident for the whole length
of the molecule in Figure 1b, whereas three colors (helices I, II and III from one BTX molecule)
can be seen at the left in Figure 1c, and three different colors (helices IV, V and VI from the
other BTX molecule) are visible at the right. We present gel electrophoresis data that
demonstrate the robust character and surface properties of the BTX molecules. In addition, we
present atomic force microscopy (AFM) data that establish the ability of all of these species
to form long tube-like species.