A blue protein as an inactivating factor for nitrite reductase from Alcaligenes faecalis strain S-6

A blue protein with a molecule weight of 12,000 containing 1 atom of type I Cu2+ was purified and crystallized from a denitrifying bacterium, Alcaligenes faecalis strain S-6, as an inactivating factor for copper-containing nitrite reductase of the same organism. Inactivation of the enzyme occurred when the enzyme was incubated aerobically with a catalytic amount of the blue protein in the presence of reducing agents such as cysteine and ascorbate. The blue protein acts as a direct electron donor for the enzyme to catalyze the reduction of nitrite, but in the absence of nitrite, the enzyme-reduced blue protein system reacts with oxygen to produce H2O2. A suicide inactivation mechanism of the enzyme due to this H2O2 production is proposed.     

Engineered protein A ligands,derived from a histidine-scanning library,facilitate the affinity purification of IgG under mild acidic conditions

Background

In antibody purification processes, the acidic buffer commonly used to elute the bound antibodies during conventional affinity chromatograph, can damage the antibody. Herein we describe the development of several types of affinity ligands which enable the purification of antibodies under much milder conditions.

Results

Staphylococcal protein A variants were engineered by using both structure-based design and combinatorial screening methods. The frequency of amino acid residue substitutions was statistically analyzed using the sequences isolated from a histidine-scanning library screening. The positions where the frequency of occurrence of a histidine residue was more than 70% were thought to be effective histidine-mutation sites. Consequently, we identified PAB variants with a D36H mutation whose binding of IgG was highly sensitive to pH change.

Conclusion

The affinity column elution chromatograms demonstrated that antibodies could be eluted at a higher pH (?pH**≧2.0) than ever reported (?pH?=?1.4) when the Staphylococcal protein A variants developed in this study were used as affinity ligands. The interactions between Staphylococcal protein A and IgG-Fab were shown to be important for the behavior of IgG bound on a SpA affinity column, and alterations in the affinity of the ligands for IgG-Fab clearly affected the conditions for eluting the bound IgG. Thus, a histidine-scanning library combined with a structure-based design was shown to be effective in engineering novel pH-sensitive proteins.

     

Rad18 guides poleta to replication stalling sites through physical interaction and PCNA monoubiquitination

The DNA replication machinery stalls at damaged sites on templates, but normally restarts by switching to a specialized DNA polymerase(s) that carries out translesion DNA synthesis (TLS). In human cells, DNA polymerase eta (poleta) accumulates at stalling sites as nuclear foci, and is involved in ultraviolet (UV)-induced TLS. Here we show that poleta does not form nuclear foci in RAD18(-/-) cells after UV irradiation. Both Rad18 and Rad6 are required for poleta focus formation. In wild-type cells, UV irradiation induces relocalization of Rad18 in the nucleus, thereby stimulating colocalization with proliferating cell nuclear antigen (PCNA), and Rad18/Rad6-dependent PCNA monoubiquitination. Purified Rad18 and Rad6B monoubiquitinate PCNA in vitro. Rad18 associates with poleta constitutively through domains on their C-terminal regions, and this complex accumulates at the foci after UV irradiation. Furthermore, poleta interacts preferentially with monoubiquitinated PCNA, but poldelta does not. These results suggest that Rad18 is crucial for recruitment of poleta to the damaged site through protein-protein interaction and PCNA monoubiquitination.     

A 5-bp Insertion in Mip Causes Recessive Congenital Cataract in KFRS4/Kyo Rats

We discovered a new cataract mutation, kfrs4, in the Kyoto Fancy Rat Stock (KFRS) background. Within 1 month of birth, all kfrs4/kfrs4 homozygotes developed cataracts, with severe opacity in the nuclei of the lens. In contrast, no opacity was observed in the kfrs4/+ heterozygotes. We continued to observe these rats until they reached 1 year of age and found that cataractogenesis did not occur in kfrs4/+ rats. To define the histological defects in the lenses of kfrs4 rats, sections of the eyes of these rats were prepared. Although the lenses of kfrs4/kfrs4 homozygotes showed severely disorganised fibres and vacuolation, the lenses of kfrs4/+ heterozygotes appeared normal and similar to those of wild-type rats. We used positional cloning to identify the kfrs4 mutation. The mutation was mapped to an approximately 9.7-Mb region on chromosome 7, which contains the Mip gene. This gene is responsible for a dominant form of cataract in humans and mice. Sequence analysis of the mutant-derived Mip gene identified a 5-bp insertion. This insertion is predicted to inactivate the MIP protein, as it produces a frameshift that results in the synthesis of 6 novel amino acid residues and a truncated protein that lacks 136 amino acids in the C-terminal region, and no MIP immunoreactivity was observed in the lens fibre cells of kfrs4/kfrs4 homozygous rats using an antibody that recognises the C- and N-terminus of MIP. In addition, the kfrs4/+ heterozygotes showed reduced expression of Mip mRNA and MIP protein and the kfrs4/kfrs4 homozygotes showed no expression in the lens. These results indicate that the kfrs4 mutation conveys a loss-of-function, which leads to functional inactivation though the degradation of Mip mRNA by an mRNA decay mechanism. Therefore, the kfrs4 rat represents the first characterised rat model with a recessive mutation in the Mip gene.     

Vasoprotective Effects of Urocortin 1 against Atherosclerosis In Vitro and In Vivo

Aim

Atherosclerosis is the complex lesion that consists of endothelial inflammation, macrophage foam cell formation, vascular smooth muscle cell (VSMC) migration and proliferation, and extracellular matrix production. Human urocortin 1 (Ucn1), a 40-amino acid peptide member of the corticotrophin-releasing factor/urotensin I family, has potent cardiovascular protective effects. This peptide induces potent and long-lasting hypotension and coronary vasodilation. However, the relationship of Ucn1 with atherosclerosis remains unclear. The present study was performed to clarify the effects of Ucn1 on atherosclerosis.

Methods

We assessed the effects of Ucn1 on the inflammatory response and proliferation of human endothelial cells (ECs), human macrophage foam cell formation, migration and proliferation of human VSMCs, extracellular matrix expression in VSMCs, and the development of atherosclerosis in apolipoprotein E-deficient (Apoe ^−/−) mice.

Results

Ucn1 significantly suppressed cell proliferation without inducing apoptosis, and lipopolysaccharide-induced up-regulation of monocyte chemoattractant protein-1 and intercellular adhesion molecule-1 in human ECs. Ucn1 significantly reduced oxidized low-density lipoprotein-induced foam cell formation with a significant down-regulation of CD36 and acyl-CoA:cholesterol acyltransferase 1 in human monocyte-derived macrophages. Ucn1 significantly suppressed the migration and proliferation of human VSMCs and increased the activities of matrix metalloproteinase-2 (MMP2) and MMP9 in human VSMCs. Intraperitoneal injection of Ucn1 into Apoe ^−/− mice for 4 weeks significantly retarded the development of aortic atherosclerotic lesions.

Conclusions

This study provided the first evidence that Ucn1 prevents the development of atherosclerosis by suppressing EC inflammatory response and proliferation, macrophage foam cell formation, and VSMC migration and proliferation. Thus, Ucn1 could serve as a novel therapeutic target for atherosclerotic cardiovascular diseases.     

An N-terminal 78 amino acid truncation of REIC/Dkk-3 effectively induces apoptosis

Overexpression of REIC/Dkk-3 (a tumor suppressor gene) induces cancer cell apoptosis through endoplasmic reticulum (ER) stress. Therefore, the identification of the portion of REIC/Dkk-3 that causes ER stress may be essential for the development of cancer treatment based on REIC/Dkk-3. Here, we made several truncated forms of REIC/Dkk-3 and investigated their therapeutic potentials against prostate cancer. Among three truncated forms, a variant comprising the N-terminal 78 amino acid region of REIC/Dkk-3 (^1-78REIC/Dkk-3) most strongly induced ER stress and apoptosis in human prostate cancer cells (PC3). For in vivo gene expression, we coupled a biodegradable polymer with naked DNA, which attained robust trans-gene expression in PC3-derived subcutaneous tumor. In therapeutic experiments, we demonstrated that multiple direct injections of polymer-conjugated ^1-78REIC/Dkk-3 plasmid provoke ER stress and significantly reduced the subcutaneous tumor volume compared with the control group. We suggest this non-viral strategy may be an effective alternative to viral gene therapy.     

Understanding substrate specificity of polyketide synthase modules by generating hybrid multimodular synthases

Modular polyketide biosynthesis can be harnessed to generate rationally designed complex natural products through bioengineering. A detailed understanding of the features that govern transfer and processing of polyketide biosynthetic intermediates is crucial to successfully engineer new polyketide pathways. Previous studies have shown that substrate stereochemistry and protein-protein interactions between polyketide synthase modules are both important factors in this process. Here we investigated the substrate tolerance of different polyketide modules and assessed the relative importance of inter-module chain transfer versus chain elongation activity of some of these modules. By constructing a variety of hybrid modular polyketide synthase systems and assaying their ability to generate polyketide products, it was determined that the substrate tolerance of each individual ketosynthase domain is an important parameter for the successful recombination of polyketide synthase modules. Surprisingly, however, failure by a module to process a candidate substrate was not due to its inability to bind to it. Rather, it appeared to result from a blockage in carbon-carbon bond formation, suggesting that proper orientation of the initially formed acyl thioester in the ketosynthase active site was important for the enzyme-catalyzed decarboxylative condensation reaction.     

Essential 110Cys in active site of membrane-associated prostaglandin E synthase-2

The amino acid sequence of membrane-associated prostaglandin (PG) E synthase-2 (mPGE synthase-2), which has a broad specificity in its thiol requirement for a catalytic activity, has the consensus region from 104Leu to 120Leu found in glutaredoxin and of thioredoxin. The sequence of Cys-x-x-Cys in the consensus region is the active site for thioredoxin and mPGE synthase-2 also has this amino acid sequence (110Cys-x-x-113Cys). The mutation from 110Cys to Ser or the double mutation from 110Cys and 113Cys to Ser caused loss of PGE synthase activity, whereas the single mutation from 113Cys to Ser did not affect the enzyme activity. These results indicate that 110Cys, but not 113Cys, is the essential amino acid in the active site of mPGE synthase-2. 110Cys is an important amino acid in PGE synthase activity and plays the critical role as Cys at the same position in redoxin. Moreover, we found that the reduced form of lipoic acid (dihydrolipoic acid) serves as one of the natural activators of mPGE synthase-2 in the cells.