α-Helicalcoiled coils represent a widespread protein structure motif distinguished by a seven-
residue periodicity of apolar residues in the primary sequence. A characteristic “knobs-into-
holes” packing of these residues into a hydrophobic core results in a superhelical, usually
left-handed, rope of two or more α-helices. Such a geometry can be parameterized. For this
purpose, a new computer program, TWISTER, was developed. With the three-dimensional
coordinates as input, TWISTER uses an original algorithm to determine the local coiled-coil …