Enzymatic ligation for synthesis of single‐chain analogue of monellin by transglutaminase*

Monellin, a sweet protein, consists of two noncovalently associated polypeptide chains: an A chain of 44 amino acid residues and a B chain of 50 residues. Microbial transglutaminase (MTGase) was used for ligation of the monellin subunits without any protecting groups, and without activation of the C^α‐carboxyl group at the C‐terminus. Since a peptide fragment LLQG is a good substrate for MTGase to form an amide bond between the γ‐amide group of the Gln residue and the ε‐amino group of Lys, a monellin B chain analogue in which LLQG was elongated at the C‐terminus (B‐LLQG) was synthesized by solid‐phase synthesis. The monellin A chain analogue in which KGK was elongated at the N‐terminus (KGK‐A) was synthesized by the same method as that of the B chain analogue. The KGK‐A chain and the B‐LLQG chain were coupled by MTGase to give single‐chain analogue of monellin. The single‐chain analogue of monellin was characterized by analytical reverse phase high performance liquid chromatography, electrospray ionization, and amino acid analyses. All analyses gave satisfactory results. The single‐chain analogue of monellin was more heat stable than natural monellin. © 1999 John Wiley & Sons, Inc. Biopoly 50: 193–200, 1999     

Identification of a member of the serralysin family isolated from a psychrotrophic bacterium, Pseudomonas fluorescens 114.

An extracellular metalloprotease named No. 114 protease is one of the major secretions of a psychrotrophic bacterium, Pseudomonas fluorescens 114, the cold-adaptation mechanism of which has not been identified. In this study, we purified and cloned No. 114 protease, which is a single polypeptide having a molecular mass of 47 kDa. This protease contains a zinc-binding motif (HEXXHXUGUXH: X, arbitrary amino acid; U, bulky hydrophobic amino acid), glycine-rich repeats (GGXGXD) and no cysteine residue, which are the features specifically found in serralysin subfamily. No. 114 protease has its maximum activity at the temperature of 35-40 degrees C, which is about 20 degrees C lower than that of a serralysin from a mesophilic bacterium, Pseudomonas aeruginosa. All these results imply that No. 114 protease from this psychrophilic bacterium is a unique member of the serralysin group characterized by a low optimal temperature.     

DNA scission and repair during pachytene in Lilium

Sedimentation characteristics of native and denatured DNA were determined for sequential stages of meiosis in Lilium. Degradation of DNA during its preparation for analysis was minimized by extracting it from meiocytes that had been converted to protoplasts. Native DNA sedimented with a major peak in the 250s region of a glycerol gradient. The profiles for all meiotic stages were essentially the same. Denatured DNA showed a bimodal profile at pachytene (104s and 62s) and a more or less unimodal profile at other stages (104s). The difference was consistently observed regardless of the particular techniques used for preparation and measurement. The 62s component was not observed in achiasmatic cells or in cells which had been arrested by cycloheximide at prepachytene stages. Isotopic studies of pachytene DNA synthesis showed that DNA label accumulated in the 100s region and that it was present in both the old and new strands derived from premeiotic S-phase. The significance of the endogenous nicking of DNA is related to the timing and mechanics of crossing-over.     

Synthesis,characterization, and sweetness-suppressing activities of gurmarin analogues missing one disulfide bond

The sweetness-suppressing polypeptide gurmarin isolated from Gymnema sylvestre consists of 35 amino acid residues and includes three intramolecular disulfide bonds. The roles of the three disulfide bonds were investigated by replacing each with two alanine residues by solid-phase synthesis. Nine analogues of [Ala^3,18]gurmarin, [Ala^10,23]gurmarin, and [Ala^17,33]-gurmarin were obtained. Three analogues had native disulfide bonds, while the other six had non-native disulfide bonds. The three analogues with native disulfide bonds suppressed the response to sucrose, but not those to glucose, fructose, saccharin, or glycine in rats. In contrast, the six analogues with non-native disulfide bonds did not suppress the responses to any of these sweeteners. These results suggest that the native disulfide bonds of gurmarin are necessary for interaction with the receptor protein, and that the sucrose-specific receptor site is present in rats. © 1998 John Wiley & Sons, Inc. Biopoly 46: 65–73, 1998     

Chemical synthesis and characterization of the sweet protein mabinlin II

The sweet protein mabinlin II isolated from the seeds of Capparis masaikai consists of the A chain with 33 amino acid residues and the B chain composed of 72 residues. The B chain contains two intramolecular disulfide bonds and is connected to the A chain through two intermolecular disulfide bridges. The A chain was synthesized by the stepwise fluoren-9-ylmethoxycarbonyl (Fmoc) solid-phase method in a yield of 5.9%, while the B chain was synthesized by a combination of the stepwise Fmoc solid-phase method and fragment condensation in a yield of 6.0%. Disulfide formation and combination of the A and B chains followed by purification by ion-exchange high-performance liquid chromatography (HPLC) gave mabinlin II in a yield of 47.4%. The characterization of the synthetic mabinlin II by HPLC, electrospray ionization mass spectrometry, amino acid analysis, and disulfide bond determination fully supported the expected structure. A 0.1% solution of the synthetic mabinlin II had an astringent-sweet taste. © 1998 John Wiley & Sons, Inc. Biopoly 46: 215–223, 1998     

Assignment of the disulfide bonds in the sweet protein brazzein

The thermostable sweet protein brazzein consists of 54 amino acid residues and has four intramolecular disulfide bonds, the location of which is unknown. We found that brazzein resists enzymatic hydrolysis at enzyme/substrate ratios (w/w) of 1:100-1:10 at 35–40°C for 24–48 h. Brazzein was hydrolyzed using thermolysin at an enzyme/substrate ratio of 1:1 (w/w) in water, pH 5.5. for 6 h and at 50°C. The disulfide bonds were determined, by a combination of mass spectrometric analysis and amino acid sequencing of cystine-containing peptides, to be between Cys4-Cys52, Cys16-Cys37, Cys22-Cys47, and Cys26-Cys49. These disulfide bonds contribute to its thermostability. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of the sweetness-suppressing polypeptide gurmarin and ent-Gurmarin

The sweetness-suppressing polypeptide gurmarin isolated from the leaves of Gymnema sylvestre consists of 35 amino acid residues including three intramolecular disulfide bonds. Herein, the total chemical synthesis of gurmarin was performed by the stepwise fluoren-9-ylmethoxy-carbonyl solid-phase method, the yield of reduced gurmarin being 1.9% based on the starting amino acid resin. Disulfide formation was carried out in the presence of a redox system of reduced glutathione/oxidized glutathione to give gurmarin in a yield of 35.5%. The product was identical to natural gurmarin by analytical reverse phase high performance liquid chromatography (RP-HPLC), mass spectroscopy (MS), and peptide mapping, and suppressed the responses to sucrose, D -glucose, and L -glucose in a rat. The D enantiomer (all D -amino acid gurmarin) was also synthesized, and was shown to be the mirror image of gurmarin. Interestingly, the D enantiomer (ent-gurmarin) also suppressed the responses to sucrose, D -glucose, and L -glucose in a rat. © 1996 John Wiley & Sons, Inc.