Poster Presentation 2014 International Biophysics Congress

Relationship between chain collapse and secondary structure in a partially folded protein (#487)

Masamichi Ikeguchi 1 , Kanako Nakagawa 2 , Yoshiteru Yamada 1 , Yoshitaka Matsumura 3 , Seiichi Tsukamoto 4 , Mio Yamamoto Ohtomo 1 , Hideaki Ohtomo 5 , Takahiro Okabe 1 , Kazuo Fujiwara 1
  1. Department of Bioinformatics, Soka University, Hachioji, Japan
  2. School of Bioscience and Biotechnology, Tokyo University of Technology, Hachioji, Japan
  3. Research & Development Division, TAO Health Life Pharma Co., Ltd., Kobe, Japan
  4. Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan
  5. Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Japan

Chain collapse and secondary structure formation are frequently observed during the early stages of protein folding. Is the chain collapse brought about by specific interactions between secondary structure units or is it due to polymer behavior in a poor solvent (coil-globule transition)? To answer this question, we addressed the relationship between the secondary structure and compactness for partially folded states of equine β-lactoglobulin (ELG). A single disulfide mutant (pseudo wild type) of ELG shows a compact denatured (A) state at acid pH in the presence of salt, which has been shown to be analogous to the folding intermediates. It has been shown that the A state contains a native-like β-hairpin and nonnative α-helix. On the other hand, the mutant shows an expanded conformational (C) state with nonnative α-helices at acid pH in the absence of salt. Thus, the secondary structure and the compactness seem to be correlated. We constructed a series of ELG mutants, in which individual secondary structure units in the A and C states were disrupted by proline substitutions, and measured small-angle X-ray scattering for these mutants under conditions in which they assume the A and C states. All proline mutants showed a compact conformation under the A-state conditions irrespective of secondary structure contents, indicating that chain collapse is not a result of secondary structure formation. On the other hand, the secondary structure is influenced by the compactness of polypeptide chain.