Conformation of Bovine Nerve Root P2 Protein: Characteristics of the Molecule from Circular Dichroism Spectra

Abstract: Circular dichroism (CD) was used to study the conformations of bovine nerve root P₂ basic protein, its reduced and carboxymethylated derivative (RCM-P₂), and its large cyanogen bromide fragment (CN1). Data in the far UV show that both the parent protein and RCM-P₂ have conformations dominated by a large amount of β structure. However, the CN1 peptide appears to exist in a largely unordered conformation. Since CN1 lacks short (20 residue) amino- and carboxy-terminal segments of the P₂ protein, the spectral data suggest that these regions are important for determining and/or maintaining folding of the P₂ protein in aqueous solutions. The P₂ protein was found to have a distinctive CD spectrum in the near UV. The characteristics of molar ellipticities indicate that the spectrum contains significant contributions from tyrosine residues, and that these contributions suggest different environments for the two tyrosines in P₂ protein. Both environments depend on protein conformation, since CD side chain absorptions are lost when P₂ protein is denatured with 5 M urea.