A right-handed parallel β-helix of 400 residues in 13
tightly packed coils is a major motif of the chains forming
the trimeric P22 tailspike adhesin. The β-helix domains
of three identical subunits are side-by-side in the trimer
and make predominantly hydrophilic inter-subunit contacts
(Steinbacher S et al., 1994, Science 265:383–386).
After the 13th coil the three individual β-helices
terminate and the chains wrap around each other to form
three interdigitated β-sheets organized into the walls
of a triangular prism. The β-strands then separate
and form antiparallel β-sheets, but still defining
a triangular prism in which each side is a β-sheet
from a different subunit (Seckler R, 1998, J Struct
Biol 122:216–222). The subunit interfaces are
buried in the triangular core of the prism, which is densely
packed with hydrophobic side chains from the three β-sheets.
Examination of this structure reveals that its packed core
maintains the same pattern of interior packing found in
the left-handed β-helix, a single-chain structure.
This packing is maintained in both the interdigitated parallel
region of the prism and the following antiparallel sheet
section. This oligomerization motif for the tailspike β-helices
presumably contributes to the very high thermal and detergent
stability that is a property of the native tailspike adhesin.