Non-native alpha-helix formation is not necessary for folding of lipocalin: comparison of burst-phase folding between tear lipocalin and beta-lactoglobulin.
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.
Tsukamoto
Seiichi
S
Department of Bioinformatics, Soka University, Hachioji, Tokyo 192-8577, Japan.
Yamashita
Takako
T
Yamada
Yoshiteru
Y
Fujiwara
Kazuo
K
Maki
Kosuke
K
Kuwajima
Kunihiro
K
Matsumura
Yoshitaka
Y
Kihara
Hiroshi
H
Tsuge
Hideaki
H
Ikeguchi
Masamichi
M
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism*; D054835:Lipocalin 1 / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D017354:Point Mutation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D053838:Scattering, Small Angle; D016415:Sequence Alignment; D014508:Urea / Q000378:metabolism; D014961:X-Ray Diffraction
D007782:Lactoglobulins; D054835:Lipocalin 1; D014508:Urea