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  • Title: Non-native alpha-helix formation is not necessary for folding of lipocalin: comparison of burst-phase folding between tear lipocalin and beta-lactoglobulin.
    Author: Tsukamoto S, Yamashita T, Yamada Y, Fujiwara K, Maki K, Kuwajima K, Matsumura Y, Kihara H, Tsuge H, Ikeguchi M.
    Journal: Proteins; 2009 Jul; 76(1):226-36. PubMed ID: 19137619.
    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.
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