The central domain of cytoplasmic intermediate filament (IF) proteins from vertebrates contains some 310 residues and forms a double-stranded coiled coil (rod) with a length of about 46 nm. The flanking terminal domains show a high cell type specific variability both in sequence and in length. Using Fourier transform infrared (FTIR) spectroscopy we measured secondary structures of isolated domains of type III and IV IF proteins and of the soluble tetramers and the filaments formed by type III IF proteins. The amide I spectrum of the desmin rod is virtually identical to the spectra of other coiled-coil proteins such as tropomyosin and the myosin rod. All these double-stranded coiled coils reveal spectra distinctly different from classical R-helical spectra. The spectrum of coiled coils is a triplet of approximately equally strong bands. One band occurs at normal R-helix position, while the other two are found at lower wavenumbers. Theoretical aspects of these findings are discussed in the accompanying paper by W. C. Reisdorf and S. Krimm [(1996[( ) Biochemistry 35, 1383[( -1386. The amino-terminal head domain of desmin has a multicomponent spectrum with major fractions of -sheet. The carboxy-terminal tail domains of desmin and the neurofilament proteins L and H, the latter in the phosphorylated and in the dephosphorylated forms, have very similar FTIR spectra, indicating mostly random structure. The spectrum of desmin type III protofilaments is very similar to the sum of the spectra of the three isolated domains. Polymerization into filaments seems to induce a small change in secondary structure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.