2d04

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spinqualitylabelsall models 2d04, resolution 2.76Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal structure of neoculin, a sweet protein with taste-modifying activity.

Overview

Although the majority of sweet compounds are of low molecular mass, several proteins are known to elicit sweet taste responses in humans. The, fruit of Curculigo latifolia contains a heterodimeric protein, neoculin, which has both sweetness and a taste-modifying activity that converts, sourness to sweetness. Here, we report the crystal structure of neoculin, at 2.76A resolution. This is the first well-defined tertiary structure of, a taste-modifying protein of this kind. The overall structure is quite, similar to those of monocot mannose-binding lectins. However, crucial, topological differences are observed in the C-terminal regions of both, subunits. In both subunits of neoculin, the C-terminal tails turn up to, form loops fixed by inter-subunit disulfide bonds that are not observed in, the lectins. Indeed, the corresponding regions of the lectins stretch, straight over the surface of another subunit. Such a C-terminal structural, feature as is observed in neoculin results in a decrease in, subunit-subunit interactions. Moreover, distribution of electrostatic, potential on the surface of neoculin is unique and significantly different, from those of the lectins, particularly in the basic subunit (NBS). We, have found that there is a large cluster composed of six basic residues on, the surface of NBS, and speculate that it might be involved in the, elicitation of sweetness and/or taste-modifying activity of neoculin., Molecular dynamics simulation based on the crystallography results, suggests that neoculin may adopt a widely "open" conformation at acidic, pH, while unprotonated neoculin at neutral pH is in a "closed", conformation. Based on these simulations and the generation of a docking, model between neoculin and the sweet-taste receptor, T1R2-T1R3, we propose, the hypothesis that neoculin is in dynamic equilibrium between open and, closed states, and that the addition of an acid shifts the equilibrium to, the open state, allowing ligand-receptor interaction.

About this Structure

2D04 is a Protein complex structure of sequences from Curculigo latifolia with NAG as ligand. Full crystallographic information is available from OCA.

Reference

Crystal structure of neoculin: insights into its sweetness and taste-modifying activity., Shimizu-Ibuka A, Morita Y, Terada T, Asakura T, Nakajima K, Iwata S, Misaka T, Sorimachi H, Arai S, Abe K, J Mol Biol. 2006 May 26;359(1):148-58. Epub 2006 Mar 29. PMID:16616933

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