Atom-by-atom analysis of global downhill protein folding

Protein folding is an inherently complex process involving coordination of the intricate networks of weak interactions that stabilize native three-dimensional structures. In the conventional paradigm, simple protein structures are assumed to fold in an all-or-none process that is inaccessible to experiment. Existing experimental methods therefore probe folding mechanisms indirectly. A widely used approach interprets changes in protein stability and/or folding kinetics, induced by engineered mutations, in terms of the structure of the native protein. In addition to limitations in connecting energetics with structure, mutational methods have significant experimental uncertainties and are unable to map complex networks of interactions. In contrast, analytical theory predicts small barriers to folding and the possibility of downhill folding. These theoretical predictions have been confirmed experimentally in recent years, including the observation of global downhill folding. However, a key remaining question is whether downhill folding can indeed lead to the high-resolution analysis of protein folding processes. Here we show, with the use of nuclear magnetic resonance (NMR), that the downhill protein BBL from Escherichia coli unfolds atom by atom starting from a defined three-dimensional structure. Thermal unfolding data on 158 backbone and side-chain protons out of a total of 204 provide a detailed view of the structural events during folding. This view confirms the statistical nature of folding, and exposes the interplay between hydrogen bonding, hydrophobic forces, backbone conformation and side-chain entropy. From the data we also obtain a map of the interaction network in this protein, which reveals the source of folding cooperativity. Our approach can be extended to other proteins with marginal barriers (less than 3RT), providing a new tool for the study of protein folding.     

Interpretive Systemology and Systemic Practice

Systemic Practice and Action Research -     

Enantioselectivity of the Musk Odor Sensation

1 Introduction Chiral recognition of substrates is one of the most characteristic phenomena of biological activity. And one of the most fundamental biological activities of chemical substances is their smell. In 1991, Linda Buck and Richard Axel~([1]) discovered a large multigene family that en codes odorant receptors, for which they were awarded the 2004 Nobel Prize in Medicine and Physiology. These odorant receptors are highly homologous, consist of ca. 320 amino acids, and show a heptah…     

Histamine deficiency suppresses murine haptoglobin production and modifies hepatic protein tyrosine phosphorylation

Histidine decarboxylase (HDC) synthesizes endogenous histamine from histidine in mammals. HDC- deficient mice (HDC-/-), if kept on a histamine-free diet, have no histamine in their tissues. HDC-/- mice show multiple phenotypes. In this study we show that both the constitutively expressed and turpentine-induced level of an acute-phase protein, haptoglobin, is significantly lower in the serum of HDC-/- mice compared to that of wild-type animals. This effect was abolished if HDC gene-targeted mice received histamine-rich food. No differences were found when lipopolysaccharide (LPS) was used to induce the acute-phase reaction. Using specific antibodies to phosphorylated tyrosine, we showed that protein tyrosine phosphorylation (Y-P) of ~50- and 26- to 27-kDa liver proteins is significantly decreased in HDC-/- mice, but that the difference was largely diminished if the animals were kept on a histamine-rich diet, suggesting that the phenotype with lower haptoglobin production is diet inducible. Upon in vivo treatment with LPS, Y-P band intensity decreased, regardless of the presence or absence of histamine. Identification of elements of the signalling pathway with decreased phosphorylation may elucidate the molecular background of the effect of endogenous histamine in the hepatic acute-phase reaction. Received 14 February 2001; received after revision 28 March 2001; accepted 4 April 2001     

The absence of the effect of percorten in alloxan-diabetic dogs

Zusammenfassung Es wurde in früheren Arbeiten mitgeteilt, daß die maximale tubuläre Zuckerresorption (Tmg) durch Percorten bedeutend erhöht wird. In der vorliegenden Untersuchung wird gezeigt, daß das Percorten im alloxandiabetischen Organismus keine Wirkung auf die Tmg hat.     

Ring-opening and Elimination Cooligomerization of Cyclic Carbonates and ε-Caprolactone

1Introduction Cyclic carbonates e.g. ethylene- and propylene carbonate undergo ring-opening polymerization (ROP) at elevated temperatures (＞ 100 ℃ ) in the presence of initiators such as Lewis acids, bases, or transesterification catalysts to yield poly(ether carbonates) as outlined below. See Fig. 1.