C-terminal domain of the Uup ATP-binding cassette ATPase is an essential folding domain that binds to DNA

The Uup protein belongs to a subfamily of soluble ATP-binding cassette (ABC) ATPases that have been implicated in several processes different from transmembrane transport of molecules, such as transposon precise excision. We have demonstrated previously that Escherichia coli Uup is able to bind DNA. DNA binding capacity is lowered in a truncated Uup protein lacking its C-terminal domain (CTD), suggesting a contribution of CTD to DNA binding. In the present study, we characterize the role of CTD in the function of Uup, on its overall stability and in DNA binding. To this end, we expressed and purified isolated CTD and we investigated the structural and functional role of this domain. The results underline that CTD is essential for the function of Uup, is stable and able to fold up autonomously. We compared the DNA binding activities of three versions of the protein (Uup, UupΔCTD and CTD) by an electrophoretic mobility shift assay. CTD is able to bind DNA although less efficiently than intact Uup and UupΔCTD. These observations suggest that CTD is an essential domain that contributes directly to the DNA binding ability of Uup.     

Myokine IL-15 regulates the crosstalk of co-cultured porcine skeletal muscle satellite cells and preadipocytes

The present study was carried out to preliminarily reveal the underlying mechanisms of the co-culture system between porcine muscle satellite cells (SCs) and stromal-vascular cells (SVs). The two cell types were co-cultured to assess both proliferation and differentiation. Desmin and Pref-1 immunofluorescence staining technique were taken to identify the two types of isolated cells. The expression of specific marker genes Myogenin was up-regulated in SCs (P < 0.05) and the differentiation of SCs could be promoted when co-cultured with preadipocytes compared with the single-cultured control, while expression of c/EBPβ in SVs was down-regulated (P < 0.05) and the differentiation of preadipocytes could be inhibited. Furthermore, secretion of myokine IL-15 was markedly increased, as well as its gene and protein expression levels in co-culture supernatants. However, the secretion of adipokine leptin was significantly decreased. These findings demonstrate that myokines like IL-15 could facilitate the SCs’ differentiation while inhibit the SVs differentiation, and act as an important regulator of co-culture between muscle cells and adipocytes.     

脉冲电场对人红细胞膜结构影响的冷冻断裂研究

对外加脉冲电场处理的人红血球冷冻断裂和蚀刻的复型观察中发现在强电场(3KV/cm)作用下,细胞周围有颗粒状和纤维状结构。结合SDS电泳分析证明了它们是由于在电场作用下,红血球膜的带3蛋白和膜骨架蛋白(血影蛋白)脱出的结果。在强电场作用下,由于膜蛋白和膜骨架蛋白的脱出造成了对细胞膜的损伤,使细胞膜稳定性降低,细胞易变形和形成伪足。由于膜蛋白的脱出,多余的自由脂质进入细胞质内而形成泡状结构。外电场改变了蛋白-蛋白以及蛋白-脂分子间的作用可能是电穿孔的主要机理。本文还对当前公认的冷冻断裂中所观察到的膜中间颗粒的来源提出了疑问,并提出了它们还可能与冰晶有关。而冰晶的形成又与膜的亲水与疏水性有关。     

Significance of the immune response to a major, conformational B-cell epitope on the hepatitis C virus NS3 region defined by a human monoclonal antibody.

The nonstructural protein NS3 of hepatitis C virus (HCV) possesses two enzymatic domains which are thought to be essential for the virus life cycle: an N-terminal serine-type proteinase, responsible for the processing of nonstructural polypeptides, and a C-terminal nucleoside triphosphatase/helicase, presumably involved in the unwinding of the viral genome. The human antibody response to NS3 usually appears early in the course of HCV infection and is predominantly directed against the carboxyl-terminal portion; however, its fine specificity and clinical significance are largely unknown. We have generated a human monoclonal antibody (hMAb), designated CM3.B6, from a cloned B-cell line obtained from the peripheral blood of a patient with chronic HCV infection, which selectively recognized the purified NS3 protein expressed in bacteria or in eukaryotic cells transfected with full-length or NS3 cDNA. Fine-specificity studies revealed that CM3.B6 recognized a 92-amino-acid sequence (clone 8, amino acids 1363 to 1454) selected from an NS3 DNase fragment library but failed to bind to 12-mer peptides synthesized from the same region, suggesting recognition of a conformational B-cell epitope. Experiments using deletion mutants of clone 8 and competitive inhibition studies using a panel of NS3 peptide-specific murine MAbs indicated that limited N-terminal and C-terminal deletions resulted in a significant reduction of hMAb binding to clone 8, thus identifying a minimal antibody binding domain within clone 8. Competition experiments showed that binding of CM3.B6 to the NS3 protein was efficiently inhibited by 39 of 44 (89%) sera from HCV-infected patients, suggesting that the hMAb recognized an immunodominant epitope within the NS3 region. More importantly, recognition of the sequence defined by CM3.B6 appeared to accurately discriminate between viremic and nonviremic anti-HCV positive sera, suggesting potentially relevant clinical applications in the diagnosis and treatment of HCV infection.     

Theoretical Insights into Catalytic Mechanism of Protein Arginine Methyltransferase 1

Protein arginine methyltransferase 1 (PRMT1), the major arginine asymmetric dimethylation enzyme in mammals, is emerging as a potential drug target for cancer and cardiovascular disease. Understanding the catalytic mechanism of PRMT1 will facilitate inhibitor design. However, detailed mechanisms of the methyl transfer process and substrate deprotonation of PRMT1 remain unclear. In this study, we present a theoretical study on PRMT1 catalyzed arginine dimethylation by employing molecular dynamics (MD) simulation and quantum mechanics/molecular mechanics (QM/MM) calculation. Ternary complex models, composed of PRMT1, peptide substrate, and S-adenosyl-methionine (AdoMet) as cofactor, were constructed and verified by 30-ns MD simulation. The snapshots selected from the MD trajectory were applied for the QM/MM calculation. The typical S_N2-favored transition states of the first and second methyl transfers were identified from the potential energy profile. Deprotonation of substrate arginine occurs immediately after methyl transfer, and the carboxylate group of E144 acts as proton acceptor. Furthermore, natural bond orbital analysis and electrostatic potential calculation showed that E144 facilitates the charge redistribution during the reaction and reduces the energy barrier. In this study, we propose the detailed mechanism of PRMT1-catalyzed asymmetric dimethylation, which increases insight on the small-molecule effectors design, and enables further investigations into the physiological function of this family.     

Oxidative stress induces autophagic cell death independent of apoptosis in transformed and cancer cells

Autophagy is a self-digestion process that degrades intracellular structures in response to stresses leading to cell survival. When autophagy is prolonged, this could lead to cell death. Generation of reactive oxygen species (ROS) through oxidative stress causes cell death. The role of autophagy in oxidative stress-induced cell death is unknown. In this study, we report that two ROS-generating agents, hydrogen peroxide (H(2)O(2)) and 2-methoxyestradiol (2-ME), induced autophagy in the transformed cell line HEK293 and the cancer cell lines U87 and HeLa. Blocking this autophagy response using inhibitor 3-methyladenine or small interfering RNAs against autophagy genes, beclin-1, atg-5 and atg-7 inhibited H(2)O(2) or 2-ME-induced cell death. H(2)O(2) and 2-ME also induced apoptosis but blocking apoptosis using the caspase inhibitor zVAD-fmk (benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone) failed to inhibit autophagy and cell death suggesting that autophagy-induced cell death occurred independent of apoptosis. Blocking ROS production induced by H(2)O(2) or 2-ME through overexpression of manganese-superoxide dismutase or using ROS scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid-disodium salt decreased autophagy and cell death. Blocking autophagy did not affect H(2)O(2)- or 2-ME-induced ROS generation, suggesting that ROS generation occurs upstream of autophagy. In contrast, H(2)O(2) or 2-ME failed to significantly increase autophagy in mouse astrocytes. Taken together, ROS induced autophagic cell death in transformed and cancer cells but failed to induce autophagic cell death in non-transformed cells.