title: Multiple subsets of side-chain packing in partially folded states of alpha-lactalbumins.
abstract: Photochemically induced dynamic nuclear polarization NMR pulse-labeling techniques have been used to obtain detailed information about side-chain surface accessibilities in the partially folded (molten globule) states of bovine and human alpha-lactalbumin prepared under a variety of well defined conditions. Pulse labeling involves generating nuclear polarization in the partially folded state, rapidly refolding the protein within the NMR sample tube, then detecting the polarization in the well dispersed native-state spectrum. Differences in the solvent accessibility of specific side chains in the various molten globule states indicate that the hydrophobic clusters involved in stabilizing the alpha-lactalbumin fold can be formed from interactions between a variety of different hydrophobic residues in both native and non-native environments. The multiple subsets of hydrophobic clusters are likely to result from the existence of distinct but closely related local minima on the free-energy landscape of the protein and show that the fold and topology of a given protein may be formed from degenerate groups of side chains.
authors.affiliation: Department of Chemistry, Oxford Centre for Molecular Sciences, Central Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QH, United Kingdom.
authors.forename: K Hun
authors.initials: KH
authors.lastname: Mok
authors.forename: Toshio
authors.initials: T
authors.lastname: Nagashima
authors.forename: Iain J
authors.initials: IJ
authors.lastname: Day
authors.forename: P J
authors.initials: PJ
authors.lastname: Hore
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Dobson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding
chemical_list: D007768:Lactalbumin