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.

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.

Colon stenosis due to acute neonatal appendicitis in a preterm baby: a case report.

BACKGROUND: Colon stenosis and acute appendicitis are rare diseases among premature babies. To the best of our knowledge, no study has identified both the conditions in preterm babies. CASE PRESENTATION: Here we report a case of a preterm Japanese male baby who developed ascending colon stenosis and appendicitis. During his neonatal intensive care unit stay, he developed increasing apnea and vomiting with rapidly worsening abdominal distention. Contrast radiographs indicated colon stenosis. Emergent exploratory laparotomy revealed ascending colon stenosis with appendix adhesion; both the lesions were surgically resected. The pathological findings suggested that he had appendicitis several weeks prior to the surgery; the onset of colon lesion seemed later than that of appendix. The perforated appendix was covered by the ascending colon, and inflammatory reactions led to the narrowing of the intestinal lumen. CONCLUSIONS: Neonatal appendicitis and colon stenosis are both challenging for the diagnosis, and early laparotomy is necessary when these conditions are suspected.

[Minimal change nephrotic syndrome developing in a rheumatoid arthritis patient under etanercept treatment].

A 67-year-old female patient with rheumatoid arthritis (RA) developed minimal change nephrotic syndrome (MCNS) while under treatment with etanercept (ETN). Histopathological examination of renal biopsy specimens showed minimal-change nephropathy. Almost complete resolution of the MCNS was achieved by discontinuation of ETN and initiation of steroid therapy. There have been no reports from Japan of the occurrence of MCNS caused by ETN administration in RA patients, and only very few cases have been reported from around the world. Therefore, this case was considered to be very uncommon and worthy of reporting, and herein is a report of our patient.