title: Importance of Glu53 in the C-terminal region of brazzein, a sweet-tasting protein.
abstract: BACKGROUND
  The sweetness of brazzein, one of the known sweet proteins, is dependent on charges and/or structures of its specific amino acid side chains. As the residues in the C-terminus of brazzein are known to play a critical role in sweetness, the currently unknown function of Glu53 requires further study.
  
  
  RESULTS
  To identify important residues responsible for the sweetness of the protein brazzein, four mutants of the Glu53 residue in the C-terminal region of des-pE1M-brazzein, which lacks the N-terminal pyroglutamate, were constructed using site-directed mutagenesis. Mutations of Glu53 substitution to Ala or Asp significantly decreased the sweetness. On the other hand, a Lys mutation resulted in a molecule with sweetness similar to that of des-pE1M-brazzein. Mutation of Glu53 to Arg resulted in a molecule significantly sweeter than des-pE1M-brazzein, which agrees with previous findings showing that mutation with positively charged residues results in a sweeter protein.
  
  
  CONCLUSIONS
  Our results suggest that the residue at position 53 is crucial for the sweetness of brazzein, which may be interacting with the sweet-taste receptor. © 2015 Society of Chemical Industry.
authors.affiliation: Biomolecular Chemistry Laboratory, Department of Chemistry, College of Natural Sciences, Chung-Ang University, 221 Huksuk-Dong, Dongjak-Ku, Seoul, 156-756, Korea.
authors.forename: Jin-Kyung
authors.initials: JK
authors.lastname: Lim
authors.affiliation: Biomolecular Chemistry Laboratory, Department of Chemistry, College of Natural Sciences, Chung-Ang University, 221 Huksuk-Dong, Dongjak-Ku, Seoul, 156-756, Korea.
authors.forename: Jin-Chul
authors.initials: JC
authors.lastname: Jang
authors.affiliation: Biomolecular Chemistry Laboratory, Department of Chemistry, College of Natural Sciences, Chung-Ang University, 221 Huksuk-Dong, Dongjak-Ku, Seoul, 156-756, Korea.
authors.forename: Ji-Na
authors.initials: JN
authors.lastname: Kong
authors.affiliation: Biomolecular Chemistry Laboratory, Department of Chemistry, College of Natural Sciences, Chung-Ang University, 221 Huksuk-Dong, Dongjak-Ku, Seoul, 156-756, Korea.
authors.forename: Myung-Chul
authors.initials: MC
authors.lastname: Kim
authors.affiliation: Biomolecular Chemistry Laboratory, Department of Chemistry, College of Natural Sciences, Chung-Ang University, 221 Huksuk-Dong, Dongjak-Ku, Seoul, 156-756, Korea.
authors.forename: Kwang-Hoon
authors.initials: KH
authors.lastname: Kong
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution / Q000235:genetics; D001120:Arginine / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D005973:Glutamine / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D020539:Sequence Analysis, Protein; D013329:Structure-Activity Relationship; D013549:Sweetening Agents / Q000737:chemistry*; D013649:Taste
chemical_list: D010940:Plant Proteins; D013549:Sweetening Agents; C090521:brazzein protein, Pentadiplandra brazzeana; D005973:Glutamine; D001120:Arginine
keywords: Glu53; brazzein; mutagenesis; sweetness determinant