The effect of a side chain-backbone swap on protein stability.
To assess the relative importance of backbone hydrogen bonding (H-bonding) vs. side chain hydrophobicity in protein structural formation, a method called side chain-backbone swap is proposed. Such a method swaps the side chain and backbone portions of certain amino acid residues, such as Asp, Glu, Asn, Gln, Lys, and Arg. Such a swap retains the sequence of a polypeptide and preserves the identity of the backbone linkage. On the other hand, the swap disrupts backbone H-bonding geometry because of the introduction of extra methylene groups into the peptide backbone. In this project, we chose the two-stranded alpha-helical coiled-coil to implement side chain-backbone swap. A pair of 36-residue peptides was designed. The two peptides have identical sequence with four residues in each heptad repeat occupied by glutamyl residues. Each glutamic acid was incorporated either as alpha-glutamyl residue (the peptide is denoted as alpha-Glu-36) or as gamma-glutamyl residue (the peptide is denoted as gamma-Glu-36). The inter-conversion between the two peptides constitutes a side chain-backbone swap. Residues constituting the hydrophobic core of the coiled-coil, however, are left unchanged. The peptide pair was characterized by circular dichroism spectroscopy, reversed-phase liquid chromatography (RPLC), and two-dimensional nuclear magnetic resonance (NMR). The results indicate that alpha-Glu-36 is a two-stranded alpha-helical coiled-coil while gamma-Glu-36 lacks stable structural elements. It is concluded that, at least for coiled-coils where hydrophobic interactions are predominantly long-range, local backbone H-bonding is a required for structural formation, consistent with a hierarchic folding mechanism. The methodological implication of side chain-backbone swap is also discussed.
Department of Pharmaceutics and Pharmaceutical Chemistry, University of Utah, Salt Lake City, UT 84112, USA.
K T
KT
Flinders
Y B
YB
Yu
P F
PF
Flynn
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D008279:Magnetic Resonance Imaging; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary
D000596:Amino Acids; D010455:Peptides; C490717:alpha-Glu-36 coiled coil; C490718:gamma-Glu-36 coiled coil