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Non‐native α‐helix formation is not necessary for folding of lipocalin: Comparison of burst‐phase folding between tear lipocalin and β‐lactoglobulin
Author(s) -
Tsukamoto Seiichi,
Yamashita Takako,
Yamada Yoshiteru,
Fujiwara Kazuo,
Maki Kosuke,
Kuwajima Kunihiro,
Matsumura Yoshitaka,
Kihara Hiroshi,
Tsuge Hideaki,
Ikeguchi Masamichi
Publication year - 2009
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.22340
Subject(s) - lipocalin , folding (dsp implementation) , small angle x ray scattering , circular dichroism , protein folding , crystallography , native state , chemistry , biophysics , phase (matter) , radius of gyration , helix (gastropod) , chemical physics , scattering , biochemistry , biology , physics , ecology , optics , organic chemistry , snail , electrical engineering , engineering , polymer
Tear lipocalin and β‐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 β‐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. Proteins 2009. © 2008 Wiley‐Liss, Inc.