Kenji Inaba

Synthetic insulin analogues with a long lifetime are current drug targets for the therapy of diabetic patients. The replacement of the interchain disulfide with a diselenide bridge, which is more resistant to reduction and internal bond rotation, can enhance the lifetime of insulin in the presence of the insulin-degrading enzyme (IDE) without impairing the hormonal function. The [C7U^A ,C7U^B ] variant of bovine pancreatic insulin (BPIns) was successfully prepared by using tw

Currently, it is presumed that multiple pathways in addition to that mediated by Ero1 cooperate to achieve oxidative folding of many secretory and membrane proteins in mammalian cells. The important open question is how each oxidative pathway works distinctly or redundantly in response to various cellular conditions.

The biological kingdoms have evolved elaborate systems that ensure the catalysis of protein disulfide bond (dsb) formation in the cell. Coexisting in the periplasm of Escherichia coli are the DsbA-DsbB disulfide-introducing and DsbC-DsbD disulfide-isomerizing pathways, which promote the oxidative folding of secreted proteins. Recent structural studies of DsbB have illuminated conformational dynamics involved in the effective oxidation of the extremely reduction-prone oxidase, DsbA, as well as th

Zinc ions (Zn²⁺) are imported into the early secretory pathway by Golgi-resident transporters, but their handling and functions are not fully understood. Here, we show that Zn²⁺ binds with high affinity to the pH-sensitive chaperone ERp44, modulating its localization and ability to retrieve clients like Ero1α and ERAP1 to the endoplasmic reticulum (ER). Silencing the Zn²⁺ transporters that uptake Zn²⁺ into the Golgi led to ERp44 dysfunction and increas

Recent studies have revealed numerous examples in which oxidation and reduction of cysteines in proteins are integrated into specific cascades of biological regulatory systems. In general, these reactions proceed as thiol-disulfide exchange events. However, it is not exactly understood how a disulfide bond is created de novo. DsbB, an Escherichia coli plasma membrane protein, is one of the enzymes that create a new disulfide bond within itself and in DsbA, the direct catalyst of protein disulfid

DsbB is an Escherichia coli plasma membrane protein that reoxidizes the Cys30-Pro-His-Cys33 active site of DsbA, the primary dithiol oxidant in the periplasm. Here we describe a novel activity of DsbB to induce an electronic transition of the bound ubiquinone molecule. This transition was characterized by a striking emergence of an absorbance peak at 500 nm giving rise to a visible pink color. The ubiquinone red-shift was observed stably for the DsbA(C33S)-DsbB complex as well as transiently by

The sigma(E) pathway of extracytoplasmic stress responses in Escherichia coli is activated through sequential cleavages of the anti-sigma(E) protein, RseA, by membrane proteases DegS and RseP. Without the first cleavage by DegS, RseP is unable to cleave full-length RseA. We previously showed that a PDZ-like domain in the RseP periplasmic region is essential for this negative regulation of RseP. We now isolated additional deregulated RseP mutants. Many of the mutations affected a periplasmic regi

DsbB is a disulfide oxidoreductase present in the Escherichia coli plasma membrane. Its cysteine pairs, Cys41-Cys44 and Cys104-Cys130, facing the periplasm, as well as the bound quinone molecules play crucial roles in oxidizing DsbA, the protein dithiol oxidant in the periplasm. In this study, we characterized quinone-free forms of DsbB prepared from mutant cells unable to synthesize ubiquinone and menaquinone. While such preparations lacked detectable quinones, previously reported lauroylsarcos