Ultraviolet resonance Raman spectra of solubilized connectin indicated the presence of β-sheets and hydrogen-bonded irregular structures. Some Trp and Tyr sidechains are located in hydrophobic environments and some NHs of mainchain amides and Trp indoles are not easily reached by solvent water, suggesting the presence of folded structures constructed of the β- and irregular parts. Infrared spectra showed an abundance of β-sheets in a connectin fiber, some of which were aligned with their mainchain axes parallel to the fiber axis. Thus, the β-spiral structure proposed for elastin is improbable in connectin. This conclusion is also supported by their different amide III frequencies in the visible Raman spectra. A possible filamentous structure of repeated domains, consisting of β-sheets and irregular parts, is discussed.
