Isolation and characterization of cytosolic and membrane-bound deubiquitinylating enzymes from bovine brain.

The deubiquitinylating enzymes (DUBs), that release free ubiquitin (Ub) from its precursors or ubiquitinylated proteins, are known to comprise of a large protein family in eukaryotes, but those in mammalian tissues remain largely unknown. Here we report the existence of unexpectedly large species of DUBs in both soluble and membrane-bound fractions of bovine brain, based on their ability to cleave (125)I-labeled Ub-fused alphaNH-MHISPPEPESEEEEEHYC (designated as Ub-PESTc). Two cytosolic enzymes, tentatively called sDUB-1 and sDUB-2, with molecular masses of about 30 kDa were purified to near homogeneity by Ub-Sepharose affinity chromatography. sDUB-1 and sDUB-2 corresponded to UCH-L3 and UCH-L1/PGP 9.5, respectively. Intriguingly, the particulate fraction of the brain homogenate was found to also contain strong activities against (125)I-Ub-PESTc, which can be solubilized by treatment with 5% n-heptyl-beta-D-thioglucoside and 1% Nonidet P-40, but not by washing with 1 M NaCl. From the solubilized material, two new 30-kDa, membranous DUBs (called mDUB-1 and mDUB-2) were purified to apparent homogeneity by Ub-Sepharose chromatography. Two other Ub-aldehyde sensitive DUBs, designated as mDUB-3 and mDUB-4, were also partially purified by conventional chromatographic operations. These mDUBs differed from each other in substrate specificity and exhibited different characteristics from the sDUBs, revealing that they are a new type of membrane-bound DUB. These results indicate the presence of divergent DUBs in mammalian brain, which may contribute to regulation of numerous pivotal cellular functions mediated by the covalent modification of Ub.     

Dual functions of the heartless fibroblast growth factor receptor in development of the Drosophila embryonic mesoderm

The Drosophila embryonic mesoderm forms by invagination of the ventral-most blastoderm cells. Subsequent development of this germ layer involves the dorsolateral migration of the internalized cells and expansion by cell division, followed by the specification of particular cell fates through the coordinate actions of both intrinsic and extrinsic regulatory mechanisms. The latter include several intercellular signals that function across germ layers. These processes combine to generate a diversity of mesodermal subtypes, including the cardial and pericardial cells of the heart or dorsal vessel, a complete set of somatic muscle founders each with its unique identity, a population of cells that form the visceral musculature, and other cells that develop into hemocytes and the fat body. Here, we review recent evidence for the involvement of a fibroblast growth factor receptor (FGFR) encoded by the heartless (htl) gene in early directional migration of the Drosophila mesoderm. In addition, we provide new data that 1) demonstrate a second role for Htl in promoting the specification of the precursors to certain cardiac and somatic muscle cells in the Drosophila embryo, independent of its cell migration function, 2) suggest that Ras and at least one other signal transduction pathway act downstream of Htl, and 3) establish a functional relationship between the Ras pathway and Tinman (Tin), a homeodomain factor that is essential for specifying some of the same dorsal mesodermal cells that are dependent on Htl. Finally, parallels between requirements for FGFR signaling in Drosophila and vertebrate mesoderm development are considered. Dev. Genet. 22:212–229, 1998. © 1998 Wiley-Liss, Inc.     

Remodeling of nuclear architecture during the cell cycle in Drosophila embryos

Little is known about what determines the nuclear matrix or how its reorganization is regulated during mitosis. In this study we report on a monoclonal antibody, mAb2A, which identifies a novel nuclear structure in Drosophila embryos which forms a diffuse meshwork at interphase but which undergoes a striking reorganization into a spindle-like structure during pro- and metaphase. Double labelings with α-tubulin and mAb2A antibodies demonstrate that the microtubules of the mitotic apparatus co-localize with this mAb2A labeled structure during metaphase, suggesting it may serve a role in microtubule spindle assembly and/or function during nuclear division. That the mAb2A-labeled nuclear structure is essential for cell division and/or maintenance of nuclear integrity was directly demonstrated by microinjection of mAb2A into early syncytial embryos which resulted in a disintegration of nuclear morphology and perturbation of mitosis. © 1996 Wiley-Liss, Inc.     

Isolation and characterization of a novel glycosyl hydrolase family 74 (GH74) cellulase from the black goat rumen metagenomic library

This study aimed to isolate and characterize a novel cellulolytic enzyme from black goat rumen by using a culture-independent approach. A metagenomic fosmid library was constructed from black goat rumen contents and screened for a novel cellulase. The KG37 gene encoding a protein of 858 amino acid residues (92.7 kDa) was isolated. The deduced protein contained a glycosyl hydrolase family 74 (GH74) domain and showed 77% sequence identity to two endo-1,4-β-glucanases from Fibrobacter succinogenes. The novel GH74 cellulase gene was overexpressed in Escherichia coli, and its protein product was functionally characterized. The recombinant GH74 cellulase showed a broad substrate spectrum. The enzyme exhibited its optimum activity at pH 5.0 and temperature range of 20–50 °C. The enzyme was thermally stable at pH 5.0 and at a temperature of 20–40 °C. The novel GH74 cellulase can be practically exploited to convert lignocellulosic biomass to value-added products in various industrial applications in future.     

Loss of CpSRP54 function leads to a truncated light-harvesting antenna size in Chlamydomonas reinhardtii

The Chlamydomonas reinhardtii truncated light-harvesting antenna 4 (tla4) DNA transposon mutant has a pale green phenotype, a lower chlorophyll (Chl) per cell and a higher Chl a/b ratio in comparison with the wild type. It required a higher light intensity for the saturation of photosynthesis and displayed a greater per chlorophyll light-saturated rate of oxygen evolution than the wild type. The Chl antenna size of the photosystems in the tla4 mutant was only about 65% of that measured in the wild type. Molecular genetic analysis revealed that a single plasmid DNA insertion disrupted two genes on chromosome 11 of the mutant. A complementation study identified the “chloroplast signal recognition particle 54” gene (CpSRP54), as the lesion causing the tla4 phenotype. Disruption of this gene resulted in partial failure to assemble and, therefore, lower levels of light-harvesting Chl-binding proteins in the C. reinhardtii thylakoids. A comparative in silico 3-D structure-modeling analysis revealed that the M-domain of the CpSRP54 of C. reinhardtii possesses a more extended finger loop structure, due to different amino acid composition, as compared to that of the Arabidopsis CpSRP54. The work demonstrated that CpSRP54 deletion in microalgae can serve to generate tla mutants with a markedly smaller photosystem Chl antenna size, improved solar energy conversion efficiency, and photosynthetic productivity in high-density cultures under bright sunlight conditions.     

DUB-1, a fate determinant of dynein heavy chain in B-lymphocytes, is regulated by the ubiquitin-proteasome pathway

Ubiquitination and deubiquitination of post-translational modification play counter roles in determining the fate of protein function in eukaryotic system for maintaining the cellular homeostasis. Even though novel family members of growth-regulating deubiquitinating enzymes (DUB-1 and DUB-2) have been identified, their target proteins and functions are poorly understood. Dub genes encoding DUB-1 and DUB-2 are immediate-early genes and are induced in response to cytokine stimuli rapidly and transiently. In order to explore the possible proteins regulated by DUB-1, we performed the matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis followed by immunoprecipitation. We confirmed that DUB-1 interacts with dynein heavy chain, which is known to regulate the movement of organelles and microtubule binding ability. In addition, structural and immunoprecipitation analyses revealed that DUB-1 contains a putative PEST motif and is polyubiquitinated, indicating that DUB-1 is also regulated by the ubiquitin-proteasome pathway.     

Toll-like receptor 9-stimulated monocyte chemoattractant protein-1 is mediated via JNK-cytosolic phospholipase A2-ROS signaling

Monocyte chemoattractant protein-1 (MCP-1) influences monocyte migration into sites of inflammation. This study highlights the importance of cytosolic phospholipase A2 (cPLA2)-mediated reactive oxygen species (ROS) signaling processes in the regulation of MCP-1 release as a result of toll-like receptor (TLR) activation. In macrophages, activation of TLR9 induced MCP-1 and cPLA2-phosphorylated arachidonic acid (AA) release. Inhibition of cPLA2 blocked CpG-induced MCP-1 and AA release. Although CpG stimulates phosphorylation of ERK, p38 and JNK, only inhibition of the JNK signaling pathways attenuated MCP-1 release, suggesting that the TLR9-mediated MCP-1 release was dependent upon the JNK pathway. TLR9 activation also stimulated ROS generation, while inhibition of NADPH oxidases (Noxs) blocked CpG-induced MCP-1 release. The CpG treatment increased macrophage Nox1 mRNA level, however it had no effect on macrophage Nox2 mRNA level. Overall, these results suggest that CpG enhances ROS generation through cPLA2-dependent pathways, which results in MCP-1 release.