Non-native alpha-helix formation is not necessary for folding of lipocalin: comparison of burst-phase folding between tear lipocalin and beta-lactoglobulin

Proteins. 2009 Jul;76(1):226-36. doi: 10.1002/prot.22340.

Abstract

Tear lipocalin and beta-lactoglobulin are members of the lipocalin superfamily. They have similar tertiary structures but unusually low overall sequence similarity. Non-native helical structures are formed during the early stage of beta-lactoglobulin folding. To address whether the non-native helix formation is found in the folding of other lipocalin superfamily proteins, the folding kinetics of a tear lipocalin variant were investigated by stopped-flow methods measuring the time-dependent changes in circular dichroism (CD) spectrum and small-angle X-ray scattering (SAXS). CD spectrum showed that extensive secondary structures are not formed during a burst-phase (within a measurement dead time). The SAXS data showed that the radius of gyration becomes much smaller than in the unfolded state during the burst-phase, indicating that the molecule is collapsed during an early stage of folding. Therefore, non-native helix formation is not general for folding of all lipocalin family members. The non-native helix content in the burst-phase folding appears to depend on helical propensities of the amino acid sequence.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Circular Dichroism
  • Escherichia coli / genetics
  • Humans
  • Kinetics
  • Lactoglobulins / chemistry
  • Lactoglobulins / metabolism*
  • Lipocalin 1 / chemistry
  • Lipocalin 1 / genetics*
  • Lipocalin 1 / isolation & purification
  • Lipocalin 1 / metabolism*
  • Molecular Sequence Data
  • Point Mutation
  • Protein Denaturation
  • Protein Folding
  • Protein Structure, Secondary
  • Scattering, Small Angle
  • Sequence Alignment
  • Urea / metabolism
  • X-Ray Diffraction

Substances

  • Lactoglobulins
  • Lipocalin 1
  • Urea