Hydrophobic interaction between globin helices.

The interhelical interfaces have been examined in seven high-resolution globin chains. The profiles of hydrophobic contact, as measured by the residue solvent-accessible area loss upon folding, have been calculated. The seven globins studied differ in their overall loss of solvent-accessible area upon packing of their helices, the order being 1MBD greater than 1LH1 greater than 1ECD greater than 2MHBB greater than 2HHBB greater than 2HHBA greater than 2MHBA, which gives a measure of the difference in stability due to the hydrophobic interaction. The five helix-pair packings (AH, BE, BG, FH and GH) examined in detail have qualitative similarities. There are, however, substantial quantitative differences both at the equivalent residue level and at the level of overall helix-helix contact, which has significance in some models of folding. The AH pair has the most uniform area loss over the seven globins and the largest variation in accessible area loss on packing among the five helix pairs is the GH pair. The set of residues required to produce the globin fold has been deduced from the residue area losses.