[A comparative analysis of interhelical polar interactions of various alpha-helix packings in proteins].

One hundred twenty globular proteins and forty five "leucine zippers" representing all types of packing of long alpha-helices were studied in terms of revealing and comparing their interhelical hydrogen and salt bonds. Many previous studies of "leucine zippers" and their analogs showed that interhelical interactions between polar groups could impart specificity to packing of an alpha-helix. The current comparison demonstrated that basically, globular proteins and "leucine zippers" had similar interhelical polar interactions with presumably a similar structural role. However, depending on packing of alpha-helices, the networks of interhelical polar bonds were shown to be distinct and determined both by physicochemical properties of involved amino acid residues and by the relative positions of hydrophobic and hydrophilic residues on the surface of alpha-helices. The revealed distinction is probably crucial for selecting the unique packing of an alpha-helix.