Importance of polypeptide chain length for the correct local folding of a ß-sheet protein.

ABSTRACT

Equine ß-lactoglobulin is a 162-residue ß-sheet protein. A partially folded form of equine ß-lactoglobulin contains a ß-hairpin and an α-helix. The ß-hairpin converts into non-native α-helices at temperatures <0°C. CHIBL, a truncated equine ß-lactoglobulin (residues 88-142), contains the low-temperature α-helical structure even at room temperature, indicating that the interactions responsible for the stability of the ß-hairpin reside in non-CHIBL residues. For the study reported herein, we characterized two truncated mutants and their leucine103 → proline103 variants to identify residues that stabilize the ß-hairpin. The dependence of their circular dichroism spectra on chloride ion concentration and temperature revealed that the ability to transition from the non-native α-helices to the ß-hairpin depends on the polypeptide chain length and improves as the chain length increases despite the apparent absence of any ordered structure in the extended sequences.