Structure basis of the improved sweetness and thermostability of a unique double-sites single-chain sweet-tasting protein monellin (MNEI) mutant.

Structure basis of the improved sweetness and thermostability of a unique double-sites single-chain sweet-tasting protein monellin (MNEI) mutant.
Biochimie. 2018 Sep 05;:
Authors: Zhao M, Xu X, Liu B
Abstract
The sweet protein monellin has an intensely sweet potency but limited stability. We have identified a double-sites mutant (E2N/E23A) of the single-chain monellin (MNEI) with both improved sweetness (about 3-fold) and thermostability (10 °C). However, the structural basis of its superior properties remains elusive until now. Herein we report its crystal structure at a resolution 1.90 Å. Similar to the wild-type, E2N/E23A adopts a wedge-shaped structure consisting of a five-strand β-sheet partially "wrapped" around an α-helix. However, distinguishing parts were present in the loops region, including a remarkable conformation shift from β-strand to loop around residue R39. Molecular docking revealed the persistence of conserved protein-receptor interface and formation of new intermolecular ionic bonds in the E2N/E23A-receptor complex involving the taste-active residue R39 of the sweet protein, which could account for its significant improvement of sweetness. On the other hand, a rearrangement of intramolecular interaction network including the C-H … π bond between A23 and F89 that led to enhanced hydrophobicity in the protein core, could be correlated with its improved thermostability. Furthermore, two new sweeter mutan...

Source: Biochimie - September 5, 2018 Category: Biochemistry Authors: Zhao M, Xu X, Liu B Tags: Biochimie Source Type: research