Spectroscopic investigation of structure in octarellin (a de novo protein designed to adopt the α/β-barred packing)

Abstract

We present here a spectroscopic structural characterization of octarellin, a recently reported de novo protein modelled on α/β-barrel proteins [K. Go raj, A.Renard and J.A.Martial (1990) Protein Engng, 3, 259–266]. Infrared and Raman spectra analyses of octarellin‘s secondary structure reveal the expected percentage of α-helices (30%) and a higher β-sheet content (40%) than predicted from the design. When the Raman spectra obtained with octarellin and native triosephosphate isomerase (a natural α/β-barrel) are compared, similar percentages of secondary structures are found. Thermal denaturation of octarellin monitored by CD confirms that its secondary structures are quite stable, whereas its native-like tertiary fold is not. Tyrosine residues, predicted to be partially hidden from solvent, are actually exposed as revealed by Raman and UV absorption spectra. We conclude that the attempted α/β-barrel conformation in octarellin may be loosely packed. The criteria used to design octarellin are discussed and improvements suggested.