β‐Helix core packing within the triple‐stranded oligomerization domain of the P22 tailspike

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.