Microbial production of sensory-active miraculin

• DOI: 10.1016/j.bbrc.2007.06.064
• Publication Date: 2007-06-20T11:19:08Z
• Authors: Keisuke Ito; Tomiko Asakura; Yuji Morita; Ken-ichiro Nakajima; Ayako Koizumi; Akiko Shimizu-Ibuka; Katsuyoshi Masuda; Masaji Ishiguro; Tohru Terada; Jun-ichi Maruyama; Katsuhiko Kitamoto; Takumi Misaka; Keiko Abe
• Keywords: 0303 health sciences; 03 medical and health sciences; Dose-Response Relationship, Drug; Aspergillus oryzae; Sweetening Agents; Taste; Humans; Hydrogen-Ion Concentration; Protein Engineering; Recombinant Proteins; Glycoproteins

Miraculin (MCL), a tropical fruit protein, is unique in that it has taste-modifying activity to convert sourness to sweetness, though flat in taste at neutral pH. To obtain a sufficient amount of MCL to examine the mechanism involved in this sensory event at the molecular level, we transformed Aspergillus oryzae by introducing the MCL gene. Transformants were expressed and secreted a sensory-active form of MCL yielding 2 mg/L. Recombinant MCL resembled native MCL in the secondary structure and the taste-modifying activity to generate sweetness at acidic pH. Since the observed pH-sweetness relation seemed to reflect the imidazole titration curve, suggesting that histidine residues might be involved in the taste-modifying activity. H30A and H30,60A mutants were generated using the A. oryzae-mediated expression system. Both mutants found to have lost the taste-modifying activity. The result suggests that the histidine-30 residue is important for the taste-modifying activity of MCL.