UHRF2, a Ubiquitin E3 Ligase,Acts as a Small Ubiquitin-like Modifier E3 Ligase for Zinc Finger Protein 131

Small ubiquitin-like modifier (SUMO), a member of the ubiquitin-related protein family, is covalently conjugated to lysine residues of its substrates in a process referred to as SUMOylation. SUMOylation occurs through a series of enzymatic reactions analogous to that of the ubiquitination pathway, resulting in modification of the biochemical and functional properties of substrates. To date, four mammalian SUMO isoforms, a single heterodimeric SUMO-activating E1 enzyme SAE1/SAE2, a single SUMO-conjugating E2 enzyme ubiquitin-conjugating enzyme E2I (UBC9), and a few subgroups of SUMO E3 ligases have been identified. Several SUMO E3 ligases such as topoisomerase I binding, arginine/serine-rich (TOPORS), TNF receptor-associated factor 7 (TRAF7), and tripartite motif containing 27 (TRIM27) have dual functions as ubiquitin E3 ligases. Here, we demonstrate that the ubiquitin E3 ligase UHRF2 also acts as a SUMO E3 ligase. UHRF2 effectively enhances zinc finger protein 131 (ZNF131) SUMOylation but does not enhance ZNF131 ubiquitination. In addition, the SUMO E3 activity of UHRF2 on ZNF131 depends on the presence of SET and RING finger-associated and nuclear localization signal-containing region domains, whereas the critical ubiquitin E3 activity RING domain is dispensable. Our findings suggest that UHRF2 has independent functional domains and regulatory mechanisms for these two distinct enzymatic activities.     

酸敏感离子通道与脑梗死

急性脑梗死约占全部脑卒中的70%,病死率和致残率高,且极易复发。但目前针对急性脑梗死在时间窗内溶栓、抗凝等治疗手段不能从根本上切实有效地修复受损脑组织,且伴有出血等风险。寻找脑梗死形成发展的原因并予以治疗迫在眉睫。酸中毒是引起缺血性脑损伤的重要机制。大量实验研究表明,酸中毒能加重神经元的缺血性损伤,且其梗死面积与酸中毒的程度直接相关。但缺血产生的酸中毒如何引起神经元损伤的确切机制尚不明确。最近研究发现酸中毒能激活一种在中枢及周围神经中广泛存在的膜通道,即酸敏感离子通道,它对Ca2+通透,能引起细胞内Ca2+超载,同时能激活胞内酶引起细胞内蛋白质、脂类及核酸的降解,加重缺血后脑损伤。本文就酸敏感离子通道1a与脑梗死做一综述。     

Unaltered metabolism of taurolithocholic acid with changes in composition of rat intestinal microflora

Changes in composition of both total aerobes and anaerobes of rat intestinal microflora do not appear to affect the metabolism of taurolithocholic acid.     

Amino-Terminal Charge Affects the Periplasmic Accumulation of Recombinant Heregulin/EGF Hybrids Exported Using theEscherichia coliAlkaline Phosphatase Signal Sequence

AnEscherichia coliexpression system that exploits the bacterial alkaline phosphatase (PhoA) signal sequence to translocate recombinant human epidermal growth factor (hEGF) to the periplasm was used to evaluate how changes in the composition and sequence of amino acids near the PhoA–hEGF junction influence the periplasmic accumulation of recombinant protein. A series of chimeric structural genes was generated byin vitroreplacement of hEGF sequence with analogous segments from the EGF-like domain of human heregulin (HRG), significantly altering the electrostatic character of the amino-terminal region of the mature protein. Quantitation of HRG/EGF protein inE. coliperiplasmic extracts, by RP-HPLC, showed a fourfold decrease after one of two acidic residues located in the amino-terminal region of the mature hEGF, near the PhoA junction, was replaced. An additional threefold decrease was observed when the second acidic residue was replaced with a positively charged lysine. Further extension of the amino-terminal HRG sequence, beyond the first six residues, resulted in net neutralization of a more distant EGF acidic residue with no additional effect on protein yield. The importance of having a negatively charged group in the amino-terminal region of the mature protein was confirmed when insertion of an aspartic acid near the amino-terminus of two poorly expressed hybrid protein sequences resulted in a five- to eightfold increase in their recovery from the periplasm. This study demonstrates the importance of having negatively charged residues near the fusion junction of recombinant proteins expressed inE. coliusing the PhoA signal sequence for protein export.     

Clinical manifestations of taeniasis in Taiwan aborigines.

From 1974 to 1989, a total of 24,500 aborigines at 67 villages in ten mountainous districts/towns in Taiwan were examined for the Taiwan Taenia infection and 12% were found to be infected. In order to define the clinical manifestations of taeniasis caused by the Taiwan Taenia, 1661 aborigines in ten mountainous districts were surveyed. The overall clinical rate was 76%. The clinical rate was highest among Atayal aborigines (81%), followed by Bunun (66%) and Yami (61%) aborgines and lowest among Ami aborigines (40%). Among 1153 infected people, 10% had passed gravid segments in the faeces for less than 1 year, 24% for 1-3 years, 17% for 4-5 years, 23% for 6-10 years, 16% for 11-20 years, 7% for 21-30 years, and 3% over 30 years. Twenty-six occurrences of gastrointestinal and neurological symptoms were reported by 1258 infected persons. Passing proglottides in the faeces (95%) was the most frequent sign, followed by pruritis ani (77%), nausea (46%), abdominal pain (45%), dizziness (42%), increased appetite (30%), headache (26%), etc.     

Irreversible inhibition of the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase/9-ketoprostaglandin reductase by glutathione thiosulfonate

Oxidation of glutathione disulfide by a mixture of performic and hydrochloric acids leads to the formation of several compounds that are stronger inhibitors than glutathione disulfide of the placental enzyme that possess both NADP-linked 15-hydroxyprostaglandin dehydrogenase and 9-ketoprostaglandin reductase activities. The only one of these inhibitors that has been identified is glutathione thiosulfonate. The others are unstable and may include glutathione sulfinyl sulfone and glutathione disulfone. Since the enzyme appears to have a glutathione binding site in close proximity to its active site and glutathione thiosulfonate reacts with free sulfhydryl groups, the effects of this thiosulfonate on the enzyme were examined in more detail. Glutathione thiosulfonate and methyl methanethiosulfonate cause a time-dependent irreversible inhibition of both the hydroxyprostaglandin dehydrogenase and the ketoprostaglandin reductase activities, presumably by reacting with a free sulfhydryl at the prostaglandin binding site. Experiments with PGA1-glutathione show that this sulfhydryl is not necessary for the catalytic activity of the enzyme as long as the substrate can bind at the glutathione site.     

Deactivation ofCandida rugosa lipase

Summary Deactivation ofCandida rugosa lipase was found to be complex. Hydrophobic interaction induced by iso-octane influenced the initial phase of deactivation, and increased the turn-over rate of the intermediate in the transition phase. After urea-treatment the structure of the last phase was not further influenced by thermal treatment, whereas that of initial phase was more sensitive to temperature change. Charge interaction was important in maintaining the structure during the deactivation, and especially anion charge might be a major factor.     

Cleavage of territrems by alkaline hydrogen peroxide: Isolation and characterization of the aromatic moiety of territrems

The chemical reaction of cleavaging territrem B to give 3,4,5-trimethoxy benzoic acid by alkaline hydrogen peroxide was investigated. The method was applied for confirmation of the chemical structure of the aromatic moiety of territrem A, A’, B, and B’. The physicochemical properties of the aromatic cleavage product of territrem Aindicated the structure as 3,4-methylendioxy, 5-methoxy benzoic acid (or 4-methoxy, 6-carboxy, 1, 3-benzodioxole). The experiment also gave the evidences that territrem A and A’, on the other hand territrem B and B’ have the identical aromatic moieties on their structures.     

Tn4556, a 6.8-kilobase-pair transposable element of Streptomyces fradiae.

A 6.8-kilobase-pair (kbp) transposable element (Tn4556) was found in a neomycin-producing strain of Streptomyces fradiae. This element was first observed in two 30.3-kbp plasmids (pUC1123 and pUC1124) which arose when a thiostrepton resistance gene (1 kbp) was ligated with the BclI-2 fragment (22.5 kbp) that contains the origin of replication of phage SF1. The Tn4556 segment was deleted when these plasmids were transduced into another S. fradiae host with phage SF1. These deletion plasmids (pUC1210 and pUC1211) had copy numbers of less than 1 per chromosome and were unstable. In contrast, pUC1123 and pUC1124, with copy numbers of 12 to 15 per chromosome, respectively, were relatively stable. When pUC1210 and pUC1211 were reintroduced into S. fradiae by protoplast transformation, the Tn4556 element transposed again to the plasmids at numerous new locations in either of two orientations. A copy of Tn4556 was found in the S. fradiae chromosome by hybridization studies. It appears that Tn4556 originated from the chromosome, transposed into unstable pUC1210 and pUC1211, and made stable plasmids. A temperature-sensitive hybrid plasmid carrying a viomycin resistance derivative of Tn4556 (pMT660::Tn4556::vph) was constructed. When Streptomyces lividans UC8390 containing the hybrid plasmid was grown at 39 degrees C, Tn4556::vph (Tn4560) transposed to random positions in the host chromosome.