title: Modification of the Sweetness and Stability of Sweet-Tasting Protein Monellin by Gene Mutation and Protein Engineering.
abstract: Natural sweet protein monellin has a high sweetness and low calorie, suggesting its potential in food applications. However, due to its low heat and acid resistance, the application of monellin is limited. In this study, we show that the thermostability of monellin can be improved with no sweetness decrease by means of sequence, structure analysis, and site-directed mutagenesis. We analyzed residues located in the α-helix as well as an ionizable residue C41. Of the mutants investigated, the effects of E23A and C41A mutants were most remarkable. The former displayed significantly improved thermal stability, while its sweetness was not changed. The mutated protein was stable after 30 min incubation at 85°C. The latter showed increased sweetness and slight improvement of thermostability. Furthermore, we found that most mutants enhancing the thermostability of the protein were distributed at the two ends of α-helix. Molecular biophysics analysis revealed that the state of buried ionizable residues may account for the modulated properties of mutated proteins. Our results prove that the properties of sweet protein monellin can be modified by means of bioinformatics analysis, gene manipulation, and protein modification, highlighting the possibility of designing novel effective sweet proteins based on structure-function relationships.
authors.affiliation: Department of Bioengineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Qiulei
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Bioengineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Food Science and Engineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Liu
authors.initials: L
authors.lastname: Yang
authors.affiliation: Department of Bioengineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Tianming
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Bioengineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Chenggu
authors.initials: C
authors.lastname: Cai
authors.affiliation: Department of Food Science and Engineering, Qilu University of Technology, Jinan, Shandong 250353, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D015202:Protein Engineering; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013549:Sweetening Agents / Q000737:chemistry* / Q000378:metabolism / Q000627:therapeutic use
chemical_list: D010940:Plant Proteins; D013549:Sweetening Agents