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Characterization of the unfolded state of bovine α‐lactalbumin and comparison with unfolded states of homologous proteins
Author(s) -
Wirmer Julia,
Berk Holger,
Ugolini Raffaella,
Redfield Christina,
Schwalbe Harald
Publication year - 2006
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.051974506
Subject(s) - random coil , heteronuclear molecule , lysozyme , chemistry , lactalbumin , heteronuclear single quantum coherence spectroscopy , protein folding , crystallography , folding (dsp implementation) , nuclear magnetic resonance spectroscopy , molten globule , alpha lactalbumin , protein structure , biophysics , biochemistry , circular dichroism , biology , stereochemistry , electrical engineering , engineering
The unfolded states of three homologous proteins with a very similar fold have been investigated by heteronuclear NMR spectroscopy. Secondary structure propensities as derived from interpretation of chemical shifts and motional restrictions as evidenced by heteronuclear 15 N relaxation rates have been analyzed in the reduced unfolded states of hen lysozyme and the calcium‐binding proteins bovine α‐lactalbumin and human α‐lactalbumin. For all three proteins, significant deviations from random‐coil predictions can be identified; in addition, the unfolded states also differ from each other, despite the fact that they possess very similar structures in their native states. Deviations from random‐coil motional properties are observed in the α‐ and the β‐domain in bovine α‐lactalbumin and lysozyme, while only regions within the α‐domain deviate in human α‐lactalbumin. The motional restrictions and residual secondary structure are determined both by the amino acid sequence of the protein and by residual long‐range interactions. Even a conservative single point mutation from I to L in a highly conserved region between the two α‐lactalbumins results in considerable differences in the motional properties. Given the differences in oxidative folding between hen lysozyme and α‐lactalbumin, the results obtained on the unfolded states suggest that residual long‐range interactions, i.e., those between the α‐ and the β‐domain of lysozyme, may act as nucleation sites for protein folding, while this property of residual structure is replaced by the calcium‐binding site between the domains in α‐lactalbumin.