Coiled coils of different order were investigated using infrared (IR) spectroscopy. Recently, we demonstrated that dimeric coiled coils display unique vibrational spectra with at least three separable bands instead of only one band of a classical R-helix in the amide I region.This was attributed to a distortion of the helical structure by the supercoil bending, giving rise to bands that are not observed in the undistorted helix. Here, we investigated coiled coils forming trimers, tetramers, and pentamers. These higher order coiled coils, in general, possess larger superhelical pitches, resulting in a smaller helical distortion. We found that all coiled coils studied, including the native dimeric GCN4 leucine zipper and its variants leading to parallel trimers and tetramers as well as the rod portions of fibritin (parallel trimer), R-actinin (antiparallel spectrin type trimer), and COMP (parallel pentamer), displayed the typical three band pattern of the coiled coil amide I spectra. However, the separation of these three bands and their positional deviation from the classical R-helical band position was correlated to the extent of the helical distortion as reflected by the pitch values of the supercoils. The most pronounced spectral anomaly was found for the tropomyosin dimer with a reported helical pitch of 137 Å, whereas the smallest spectral distortion was found for the pentameric COMP complex and the tetrameric leucine zipper mutant, both with a pitch of about 205 Å.Coiled coils are important oligomerization elements of proteins. They are built from R-helices carrying a sevenresidue repeat pattern (a to g) of hydrophobic and hydrophilic residues in which the hydrophobic residues occupy the first (a) and the fourth (d) positions (1). This generates a hydrophobic seam along the axis of the helix along which two or more helices align laterally in parallel or antiparallel fashion. The tight contact of neighboring helices is achieved by a "knobs into holes" arrangement of the hydrophobic residues in the interface (2). Additional stabilization of the dimer and the correct positioning with respect to register arises from ionic interactions of residues close to the interface. The "classical" form of a coiled coil is doublestranded, parallel, and in register and involves two identical chains. However, there are many other forms of coiled coils. They differ with respect to chain number and orientation and can be homo-as well as heterotypic.The fixed number of two hydrophobic residues in the seven-residue-long repeat unit, (i.e., one hydrophobic residue per 3.5 residues) resulting in an amphiphatic helix versus the slightly higher number of around 3.65 residues per turn of straight R-helix, leads to a left-handed axial shift of the hydrophobic seam around the helix. As a consequence, coiled coils display a distinct left-handed twist. Its pitch length will depend on several factors such as the primary sequence, i.e., the actual choice of hydrophilic and hydrophobic residues within the repeat units. This can res...