beta-helix core packing within the triple-stranded oligomerization domain of the P22 tailspike

A right-handed parallel beta -helix of 400 residues in 13 tightly packed co ils is a major motif of the chains forming the trimeric P22 tailspike adhes in. The beta -helix domains of three identical subunits are side-by-side in the trimer and make predominantly hydrophilic inter-subunit contacts (Stei nbacher S et al., 1994, Science 265:383-386). After the 13th coil the three individual beta -helices terminate and the chains wrap around each other t o form three interdigitated beta -sheets organized into the walls of a tria ngular prism. The beta -strands then separate and form antiparallel beta -s heets, but still defining a triangular prism in which each side is a beta - 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, wh ich is densely packed with hydrophobic side chains from the three beta -she ets. Examination of this structure reveals that its packed core maintains t he same pattern of interior packing found in the left-handed beta -helix, a single-chain structure. This packing is maintained in both the interdigita ted parallel region of the prism and the following antiparallel sheet secti on. This oligomerization motif for the tailspike beta -helices presumably c ontributes to the very high thermal and detergent stability that is a prope rty of the native tailspike adhesin.