Characterization of an Aspergillus oryzae cysteinyl dipeptidase expressed in Escherichia coli

Cysteinyl dipeptidase from Aspergillus oryzae (CdpA) was produced in Escherichia coli and purified. The enzyme showed activity specific toward cysteine-containing dipeptides, but its substrate specificity was distinct from those of other cysteinyl dipeptidases of the M20 family. It was optimally active at pH 7-8 and stable at pH 6-9 and at up to 40 °C.     

The Integrin-Linked Kinase-PINCH-Parvin Complex Supports Integrin αIIbβ3 Activation

Integrin-linked kinase (ILK) is an important signaling regulator that assembles into the heteroternary complex with adaptor proteins PINCH and parvin (termed the IPP complex). We recently reported that ILK is important for integrin activation in a Chinese hamster ovary (CHO) cell system. We previously established parental CHO cells expressing a constitutively active chimeric integrin (αIIbα6Bβ3) and mutant CHO cells expressing inactive αIIbα6Bβ3 due to ILK deficiency. In this study, we further investigated the underlying mechanisms for ILK-dependent integrin activation. ILK-deficient mutant cells had trace levels of PINCH and α-parvin, and transfection of ILK cDNA into the mutant cells increased not only ILK but also PINCH and α-parvin, resulting in the restoration of αIIbα6Bβ3 activation. In the parental cells expressing active αIIbα6Bβ3, ILK, PINCH, and α-parvin were co-immunoprecipitated, indicating the formation of the IPP complex. Moreover, short interfering RNA (siRNA) experiments targeting PINCH-1 or both α- and β-parvin mRNA in the parent cells impaired the αIIbα6Bβ3 activation as well as the expression of the other components of the IPP complex. In addition, ILK mutants possessing defects in either PINCH or parvin binding failed to restore αIIbα6Bβ3 activation in the mutant cells. Kindlin-2 siRNA in the parental cells impaired αIIbα6Bβ3 activation without disturbing the expression of ILK. For CHO cells stably expressing wild-type αIIbβ3 that is an inactive form, overexpression of a talin head domain (THD) induced αIIbβ3 activation and the THD-induced αIIbβ3 activation was impaired by ILK siRNA through a significant reduction in the expression of the IPP complex. In contrast, overexpression of all IPP components in the αIIbβ3-expressing CHO cells further augmented THD-induced αIIbβ3 activation, whereas they did not induce αIIbβ3 activation without THD. These data suggest that the IPP complex rather than ILK plays an important role and supports integrin activation probably through stabilization of the active conformation.     

DNA damage sensible engineered promoter for cellular biosensing of cytotoxicity

We have established a cytotoxic sensor cell line by transfecting HepG2 cells with a luciferase protein plasmid derived from the heat shock protein 70B′ (HSP70B′) promoter, which is induced by cytotoxic reagents. HSP70B genes are up‐regulated by a wide‐range of cytotoxic stimulators, in particular, those that denature proteins. However, the HSP70B genes do not respond to DNA damage. We used a PCR array to detect marker genes of DNA damage‐related cytotoxic stimulation and found the BTG2 gene to be one such gene. Analysis of the BTG2 gene functional promoter region by transfection of various deletion constructs into HepG2 cells indicated that the p53 and NFY biding sites on BTG2 are important for the response to DNA damage. We then constructed HepG2 sensor cells using the functional BTG2 promoter, and found that these sensor cells can specifically detect the cytotoxicity accompanied by DNA strand breaks with high sensitivity. Biotechnol. Bioeng. 2009;102: 1460–1465. © 2008 Wiley Periodicals, Inc.     

Divalent Metal Ion-Induced Folding Mechanism of RNase H1 from Extreme Halophilic Archaeon Halobacterium sp. NRC-1

RNase H1 from Halobacterium sp. NRC-1 (Halo-RNase H1) is characterized by the abundance of acidic residues on the surface, including bi/quad-aspartate site residues. Halo-RNase H1 exists in partially folded (I) and native (N) states in low-salt and high-salt conditions respectively. Its folding is also induced by divalent metal ions. To understand this unique folding mechanism of Halo-RNase H1, the active site mutant (2A-RNase H1), the bi/quad-aspartate site mutant (6A-RNase H1), and the mutant at both sites (8A-RNase H1) were constructed. The far-UV CD spectra of these mutants suggest that 2A-RNase H1 mainly exists in the I state, 6A-RNase H1 exists both in the I and N states, and 8A-RNase H1 mainly exists in the N state in a low salt-condition. These results suggest that folding of Halo-RNase H1 is induced by binding of divalent metal ions to the bi/quad-aspartate site. To examine whether metal-induced folding is unique to Halo-RNase H1, RNase H2 from the same organism (Halo-RNase H2) was overproduced and purified. Halo-RNase H2 exists in the I and N states in low-salt and high-salt conditions respectively, as does Halo-RNase H1. However, this protein exists in the I state even in the presence of divalent metal ions. Halo-RNase H2 exhibits junction ribonuclease activity only in a high-salt condition. A tertiary model of this protein suggests that this protein does not have a quad-aspartate site. We propose that folding of Halo-RNase H1 is induced by binding of divalent metal ion to the quad-aspartate site in a low-salt condition.     

The optical interconversion of the P-450 and P-420 forms of neuronal nitric oxide synthase: effects of sodium cholate, mercury chloride and urea

We investigated whether or not neuronal nitric oxide synthase (nNOS) (EC 1.14.13.39) was converted to the P-420 form on exposure to sodium cholate, mercury chloride or urea, and the reconversion of the P-420 to the P-450 form. Sodium cholate and mercury chloride induced the conversion of nNOS from the P-450 to the P-420 form in concentration- and incubation time-dependent manners, and the nNOS activity decreased. In the presence of glycerol, L-arginine and/or tetrahydrobiopterin, the sodium cholate-treated P-420 form could be reconverted to the P-450 form under constant experimental conditions, and the nNOS activity could also be restored. The mercury chloride-treated P-420 form of nNOS could be reconverted to the P-450 form on incubation with reduced glutathione (GSH) or L-cysteine, and the nNOS activity was recovered. However, no reconversion of the mercury chloride-treated P-420 form to the P-450 form was observed in the presence of glycerol, L-arginine, or tetrahydrobiopterin. Urea (4.0 M) dissociated nNOS into its subunits, but nNOS remained in the P-450 form. The nNOS monomer was more susceptible to sodium cholate. After removing the urea by dialysis, and supplementation of the nNOS solution with glycerol, L-arginine or BH(4), the P-420 was reconverted to the P-450 form, and the reassociation of nNOS monomers was also observed. These results suggested that nNOS was more stable as to exposure to sodium cholate, mercury chloride or urea in comparison to microsomal cytochrome P-450, which may be due to the different heme environment and protein structure.     

Photoresponsive PEG-anthracene grafted hyaluronan as a controlled-delivery biomaterial

Ophthalmic drug delivery to the posterior segment of the eye could benefit from a responsive controlled drug delivery system with light or laser inducible changes. For example, the delivery of age-related macular degeneration drugs requires invasive monthly injections making long-term photoresponsive drug delivery a desirable option. The feasibility of this may be facilitated by both the transparency of the eye and the advanced technology in ophthalmic lasers. Hyaluronic acid photogels that are compatible with retinal pigment epithelial cell lines are shown here to deliver a variety of small and large model drugs over the long term (months). Varying UV exposures resulted in decreases/increases or the turning off and on of delivery, potentially allowing the therapy to be tailored to suit the patient and the disease.     

Imipramine inhibition of TRPM‐like plasmalemmal Mg2+ transport in vascular smooth muscle cells

Depression is associated with vascular disease, such as myocardial infarction and stroke. Pharmacological treatments may contribute to this association. On the other hand, Mg²⁺ deficiency is also known to be a risk factor for the same category of diseases. In the present study, we examined the effect of imipramine on Mg²⁺ homeostasis in vascular smooth muscle, especially via melastatin‐type transient receptor potential (TRPM)‐like Mg²⁺‐permeable channels. The intracellular free Mg²⁺ concentration ([Mg²⁺]_i) was measured using ³¹P‐nuclear magnetic resonance (NMR) in porcine carotid arteries that express both TRPM6 and TRPM7, the latter being predominant. pH_i and intracellular phosphorus compounds were simultaneously monitored. To rule out Na⁺‐dependent Mg²⁺ transport, and to facilitate the activity of Mg²⁺‐permeable channels, experiments were carried out in the absence of Na⁺ and Ca²⁺. Changing the extracellular Mg²⁺ concentration to 0 and 6 mM significantly decreased and increased [Mg²⁺]_i, respectively, in a time‐dependent manner. Imipramine statistically significantly attenuated both of the bi‐directional [Mg²⁺]_i changes under the Na⁺‐ and Ca²⁺‐free conditions. This inhibitory effect was comparable in influx, and much more potent in efflux to that of 2‐aminoethoxydiphenyl borate, a well‐known blocker of TRPM7, a channel that plays a major role in cellular Mg²⁺ homeostasis. Neither [ATP]_i nor pH_i correlated with changes in [Mg²⁺]_i. The results indicate that imipramine suppresses Mg²⁺‐permeable channels presumably through a direct effect on the channel domain. This inhibitory effect appears to contribute, at least partially, to the link between antidepressants and the risk of vascular diseases.     

The AAA-ATPase VPS4 regulates extracellular secretion and lysosomal targeting of α-synuclein

Many neurodegenerative diseases share a common pathological feature: the deposition of amyloid-like fibrils composed of misfolded proteins. Emerging evidence suggests that these proteins may spread from cell-to-cell and encourage the propagation of neurodegeneration in a prion-like manner. Here, we demonstrated that α-synuclein (αSYN), a principal culprit for Lewy pathology in Parkinson's disease (PD), was present in endosomal compartments and detectably secreted into the extracellular milieu. Unlike prion protein, extracellular αSYN was mainly recovered in the supernatant fraction rather than in exosome-containing pellets from the neuronal culture medium and cerebrospinal fluid. Surprisingly, impaired biogenesis of multivesicular body (MVB), an organelle from which exosomes are derived, by dominant-negative mutant vacuolar protein sorting 4 (VPS4) not only interfered with lysosomal targeting of αSYN but facilitated αSYN secretion. The hypersecretion of αSYN in VPS4-defective cells was efficiently restored by the functional disruption of recycling endosome regulator Rab11a. Furthermore, both brainstem and cortical Lewy bodies in PD were found to be immunoreactive for VPS4. Thus, VPS4, a master regulator of MVB sorting, may serve as a determinant of lysosomal targeting or extracellular secretion of αSYN and thereby contribute to the intercellular propagation of Lewy pathology in PD.