Tertiary Structure of α-1 Peptide of Globin Hydrolysates by the Small-Angle Solution X-ray Scattering Method

Abstract

A highly hydrophilic peptide α-1 originated from the α-chain of globin was isolated by hydrophobic chromatography. The sizes and tertiary structures of peptide α-1 monomer and aggregate were examined by the small-angle X-ray scattering (SAXS) method. The radius of gyration (Rg) of peptide α-1 in 6 M urea exhibited no concentration dependence, suggesting that peptide α-1 exists in monomeric state in this solvent. In the absence of urea the scattering patterns are composed of two components, that is, high molecular weight and low molecular weight species. The Rg of the low molecular weight component is consistent with the peptide α-1 treated with 6 M urea, indicating that this low molecular weight constituent is the monomer of peptide α-1. The Rg of the high molecular weight component increased with the peptide α-1 concentration. The weight-average molecular weight of the aggregate oligomer obtained by SAXS method was 7−9 times as large as monomer peptide α-1, which was consistent with the result by the laser light scattering study. Comparing the scattering pattern in the presence of 6 M urea with various theoretical models, the monomeric peptide α-1 took a random-coil structure and the polymer chain was distributed symmetrically. The aggregates (oligomer) of peptide α-1 also behaved as a whole in random-coil state and were formed by entanglement with the random-coil monomer. Keywords: Globin; globin hydrolysates; peptide α-1; small-angle solution X-ray scattering