Monellin (MNEI) at 1.15 A resolution.

Area of Science:

• Structural Biology
• Protein Crystallography
• Molecular Interactions

Background:

• Monellin is a natural sweet-tasting protein.
• Previous structures of monellin showed a dimer interface, which was absent in this study.
• Understanding MNEI structure is key to understanding sweet taste perception.

Purpose of the Study:

• To determine the high-resolution X-ray crystal structure of single-chain monellin (MNEI).
• To investigate the structural basis for MNEI's sweet taste.
• To explore potential interactions between MNEI and the sweet taste receptor (T1R2-T1R3).

Main Methods:

• X-ray crystallography at 1.15 A resolution.
• Refinement using anisotropic displacement parameters and riding hydrogen atoms.
• Analysis of protein structure, including side-chain conformations and bound ions.

Main Results:

• A high-resolution (1.15 A) crystal structure of MNEI was obtained.
• The structure lacked the previously observed dimer interface.
• Detailed analysis revealed alternative side-chain conformations for 38 residues and four bound negative ions, suggesting electrostatic interactions with the T1R2-T1R3 receptor.

Conclusions:

• The unique MNEI structure provides unprecedented detail.
• The absence of a dimer interface may be a key feature of this monellin variant.
• Bound ions offer new insights into MNEI's interaction with the sweet taste receptor, potentially explaining its function.