The propeptide sequence assists the correct folding required for the enzymatic activity of cocoonase.

Cocoonase, a protein that is produced by the silkworm (Bombyx mori), is thought to specifically digest the sericin protein of the cocoon and has a high homology with trypsin. Similar to trypsin, cocoonase is folded as an inactive precursor protein which is activated by releasing the propeptide moiety. However, the mechanism responsible for the activation of its catalytic structure has not yet been determined in detail. Therefore, to investigate the activation and folding mechanism of cocoonase, recombinant cocoonase (CCN) and prococoonase (proCCN) were over-expressed in E. coli cells. Both recombinant proteins (proCCN and CCN) were expressed as inclusion bodies in E. coli cells and their folding was examined under several sets of conditions. After the refolding reactions, both of the recombinant proteins were present as the oxidized soluble forms. The proCCN protein was then auto-processed to release the propeptide region for activation. Interestingly, the CCN (CCN∗) derived from the refolded proCCN showed a much stronger protease activity than the refolded CCN from the reduced CCN in a protease assay using Bz-Arg-OEt as a substrate. In addition, the secondary structure of the refolded CCN protein was similar to that of the CCN∗ protein, as evidenced by CD measurements. These results suggest that the CCN protein becomes trapped in a molten globule-like state without the assistance of the propeptide region during the folding process. We therefore conclude that the propeptide region of CCN kinetically accelerates the folding of CCN to adopt the correct conformation of cocoonase at the final step of the folding pathway.

Degradation-Suppressed Cocoonase for Investigating the Propeptide-Mediated Activation Mechanism.

Cocoonase is folded in the form of a zymogen precursor protein (prococoonase) with the assistance of the propeptide region. To investigate the role of the propeptide sequence on the disulfide-coupled folding of cocoonase and prococoonase, the amino acid residues at the degradation sites during the refolding and auto-processing reactions were determined by mass spectrometric analyses and were mutated to suppress the numerous degradation reactions that occur during the reactions. In addition, the Lys8 residue at the propeptide region was also mutated to estimate whether the entire sequence is absolutely required for the activation of cocoonase. Finally, a degradation-suppressed [K8D,K63G,K131G,K133A]-proCCN protein was prepared and was found to refold readily without significant degradation. The results of an enzyme assay using casein or Bz-Arg-OEt suggested that the mutations had no significant effect on either the enzyme activity or the protein conformation. Thus, we, herein, provide the non-degradative cocoonase protein to investigate the propeptide-mediated protein folding of the molecule. We also examined the catalytic residues using the degradation-suppressed cocoonase. The point mutations at the putative catalytic residues in cocoonase resulted in the loss of catalytic activity without any secondary structural changes, indicating that the mutated residues play a role in the catalytic activity of this enzyme.

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction.

This study shows that phosphorus sources can be recycled using the appropriate fluorous phosphine in the Wittig reaction. The designed fluorous phosphine, which has an ethylene spacer between its phosphorus atom and the perfluoroalkyl group, was synthesized from air-stable phosphine reagents. The synthesized phosphine can be used for the Wittig reaction process to obtain various alkenes in adequate yields and stereoselectivity. The concomitantly formed fluorous phosphine oxide was extracted from the reaction mixture using a fluorous biphasic system. The fluorous phosphine was regenerated by reducing the fluorous phosphine oxide with diisobutylaluminum hydride. Finally, a series of gram scale phosphorus recycling processes were performed, which included the Wittig reaction, separation, reduction, and reuse.

Photoinduced Syntheses and Reactivities of Phosphorus-Containing Interelement Compounds.

The photoinduced reactions of tetraphenyldiphosphine disulfide with a range of organic dichalcogenides successfully afforded a series of phosphorus(V)-chalcogen interelement compounds via a radical process. The relative reactivities of the organic dichalcogenides (i.e., (PhS)2, (PhSe)2, and (PhTe)2) toward the PIII or PV groups in the diphosphine analogues under light were investigated in detail, and a convenient method was developed to form P-S or P-Se interelement compounds from tetraphenyldiphosphine disulfide and (PhS)2 or (PhSe)2 upon photoirradiation. Furthermore, the relative photochemical properties and reactivities of tetraphenyldiphophine (P-P interelement compound) and its analogues toward photoinduced radical addition reactions were also discussed. The formed P-E (E = S, Se) interelement compounds could be utilized for ionic reactions, and they could be transformed into various phosphine reagents via one-pot processes.

Reductive Rearrangement of Tetraphenyldiphosphine Disulfide To Trigger the Bisthiophosphinylation of Alkenes and Alkynes.

The facile synthesis of organophosphorus compounds is of great importance for the development of new synthetic methods by using air-stable sources of phosphorus. In this respect, a synthetic method that is based on a reductive rearrangement and is capable of converting air-stable pentavalent phosphorus compounds into reactive trivalent phosphorus compounds is a powerful tool. Tetraphenyldiphosphine disulfide, which is a shelf-stable solid, was the focus of this study, and it was shown to undergo reductive rearrangement to trigger the bisthiophosphinylation of a variety of alkenes, such as terminal, cyclic, internal, and branched alkenes, 1,3-dienes, and terminal alkynes when exposed to light without any catalyst, base, or additive.

Clarification of the Dissolution Mechanism of an Indomethacin/Saccharin/Polyvinylpyrrolidone Ternary Solid Dispersion by NMR Spectroscopy.

Here, an indomethacin (IMC)/saccharin (SAC)/polyvinylpyrrolidone (PVP) ternary solid dispersion (SD) prepared by spray-drying was characterized to clarify its dissolution mechanism. Solid-state NMR spectroscopy revealed that IMC and SAC in the ternary SD interacted via hydrogen bonding in a similar manner as that in the IMC/SAC co-crystal. Initial IMC dissolution from the ternary SD was slower than that from the binary SD, although IMC supersaturation was maintained for a relatively longer time in the ternary SD. Solid- and solution-state NMR measurements for dispersed particles in the dissolution test revealed that the particle for IMC/PVP binary SD was composed of amorphous IMC dispersed in PVP matrix and α-form IMC. In contrast, the particles for the ternary SPD was composed of amorphous IMC dispersed in PVP matrix and IMC/SAC co-crystals. Scanning electron microscopy indicated that in the binary SD, amorphous IMC microfiber-gel was generated on the surface of particles after the dissolution test, preventing amorphous IMC from contacting with water. In contrast, in the ternary SD, IMC/SAC co-crystals were generated on the surface of particles, and intermediate spaces were formed on the surface, which allowed water intrusion into the particles and continuous dissolution of IMC.