Structural basis for the functional and inhibitory mechanisms of β-hydroxyacyl-acyl carrier protein dehydratase (FabZ) of Plasmodium falciparum

The β-hydroxyacyl-acyl carrier protein dehydratase of Plasmodium falciparum (PfFabZ) catalyzes the third and important reaction of the fatty acid elongation cycle. The crystal structure of PfFabZ is available in hexameric (active) and dimeric (inactive) forms. However, PfFabZ has not been crystallized with any bound inhibitors until now. We have designed a new condition to crystallize PfFabZ with its inhibitors bound in the active site, and determined the crystal structures of four of these complexes. This is the first report on any FabZ enzyme with active site inhibitors that interact directly with the catalytic residues. Inhibitor binding not only stabilized the substrate binding loop but also revealed that the substrate binding tunnel has an overall shape of “U”. In the crystal structures, residue Phe169 located in the middle of the tunnel was found to be in two different conformations, open and closed. Thus, Phe169, merely by changing its side chain conformation, appears to be controlling the length of the tunnel to make it suitable for accommodating longer substrates. The volume of the substrate binding tunnel is determined by the sequence as well as by the conformation of the substrate binding loop region and varies between organisms for accommodating fatty acids of different chain lengths. This report on the crystal structures of the complexes of PfFabZ provides the structural basis of the inhibitory mechanism of the enzyme that could be used to improve the potency of inhibitors against an important component of fatty acid synthesis common to many infectious organisms.     

Interactions of MCP1 with components of the replication machinery in mammalian cells

Eukaryotic DNA replication starts with the assembly of a pre-replication complex (pre-RC) at replication origins. We have previously demonstrated that Metaphase Chromosome Protein 1 (MCP1) is involved in the early events of DNA replication. Here we show that MCP1 associates with proteins that are required for the establishment of the pre-replication complex. Reciprocal immunoprecipitation analysis showed that MCP1 interacted with Cdc6, ORC2, ORC4, MCM2, MCM3 and MCM7, with Cdc45 and PCNA. Immunofluorescence studies demonstrated the co-localization of MCP1 with some of those proteins. Moreover, biochemical studies utilizing chromatin-immunoprecipitation (ChIP) revealed that MCP1 preferentially binds replication initiation sites in human cells. Interestingly, although members of the pre-RC are known to interact with some hallmarks of heterochromatin, our co-immunoprecipitation and immunofluorescence analyses showed that MCP1 did not interact and did not co-localize with heterochromatic proteins including HP1β and MetH3K9. These observations suggest that MCP1 is associated with replication factors required for the initiation of DNA replication and binds to the initiation sites in loci that replicate early in S-phase. In addition, immunological assays revealed the association of MCP1 forms with histone H1 variants and mass spectrometry analysis confirmed that MCP1 peptides share common sequences with H1.2 and H1.5 subtypes.     

冠状-睑下缘-口内联合切口手术治疗眶-上颌-颧骨复合骨折

目的：探讨经冠状-睑下缘-口内联合切口行眶-上颌-颧骨复合骨折坚强内固定术的临床应用价值。方法：回顾性分析69例患者经冠状-睑下缘-口内联合切口行眶-上颌-颧骨复合骨折解剖复位,钛板坚强内固定。结果：69例均一期愈合,68例治疗效果优良,1例治疗效果欠佳;2例轻度睑外翻,两周后恢复正常,无额纹变浅、面神经损伤等其他并发症。结论：冠状-睑下缘-口内联合切口具有切口隐蔽、面部疤痕不明显、显露充分、并发症少等优点,是治疗眶-上颌-颧骨复合骨折的良好手术进路。     

两种联合切口手术治疗眶-上颌-颧骨复合体骨折的对比研究

目的：对比研究冠状-睑下缘-口内联合切口手术与冠状切口联合口腔前庭沟切口手术治疗眶-上颌-颧骨复合体骨折的治疗效果。方法：选取2006年10月-2010年12月眶-上颌-颧骨复合体骨折患者136例,69例患者行冠状-睑下缘-口内联合切口手术,67例行冠状切口联合口腔前庭沟切口手术,分别命名为A组和B组,比较两组患者治疗效果,治疗效果用甲级、乙级和丙级表示。结果：A组治疗效果甲级、乙级、丙级分别为65．2％、30．4％、4．4％,B组治疗效果甲级、乙级、丙级分别为46．3％、29．8％、23．9％,A组治疗效果优于B组;A组术后并发症少于B组。结论：冠状-睑下缘-口内联合切口手术比冠状切口联合口腔前庭沟切口手术更好地治疗眶-上颌-颧骨复合体骨折,治疗效果好,并发症少,能更好地实现颧骨复位。     

多基因表达系统研究进展

细胞中大多数蛋白质以亚基形式与其他蛋白装配成蛋白复合体而发挥功能.大分子蛋白复合物的结构研究和功能分析在后基因组时代成为热点,如何高效地获得多蛋白复合物是研究其功能和结构的前提.利用基因工程技术实现多个蛋白亚基在同一宿主细胞内共表达并装配成复合体是获得多蛋白复合物的有效手段.多基因表达系统在基础和应用研究中正起到越来越...     

Implications of the gene balance hypothesis for dosage compensation

Dosage compensation refers to the equal expression between the sexes despite the fact that the dosage of the X chromosome is different in males and females. In Drosophila there is a twofold upregulation of the single male X. In triple X metafemales, there is also dosage compensation, which occurs by a two-thirds downregulation. There is a concomitant reduction in expression of many autosomal genes in metafemales. The male specific lethal (MSL) complex is present on the male X chromosome. Evidence is discussed showing that the MSL complex sequesters a histone acetyltransferase to the X chromosome to mute an otherwise increased expression by diminishing the histone acetylation on the autosomes. Several lines of evidence indicate that a constraining activity occurs from the MSL complex to prevent overcompensation on the X that might otherwise occur from the high level of acetylation present. Together, the evidence suggests that dosage compensation is a modification of a regulatory inverse dosage effect that is a reflection of intrinsic gene regulatory mechanisms and that the MSL complex has evolved in reaction in order to equalize the expression on both the X and autosomes of males and females.     

The MHC I immunopeptidome conveys to the cell surface an integrative view of cellular regulation

Self/non‐self discrimination is a fundamental requirement of life. Endogenous peptides presented by major histocompatibility complex class I (MHC I) molecules represent the essence of self for CD8 T lymphocytes. These MHC I peptides (MIPs) are collectively referred to as the immunopeptidome. From a systems‐level perspective, very little is known about the origin, composition and plasticity of the immunopeptidome. Here, we show that the immunopeptidome, and therefore the nature of the immune self, is plastic and moulded by cellular metabolic activity. By using a quantitative high‐throughput mass spectrometry‐based approach, we found that altering cellular metabolism via the inhibition of the mammalian target of rapamycin results in dynamic changes in the cell surface MIPs landscape. Moreover, we provide systems‐level evidence that the immunopeptidome projects at the cell surface a representation of biochemical networks and metabolic events regulated at multiple levels inside the cell. Our findings open up new perspectives in systems immunology and predictive biology. Indeed, predicting variations in the immunopeptidome in response to cell‐intrinsic and ‐extrinsic factors could be relevant to the rational design of immunotherapeutic interventions.     

Beyond the Food Web Connections to a Deeper Industrial Ecology

Industrial ecology is a school of thought based, in part, upon a simple analogy between industrial systems and ecological systems in terms of their material and energy flows. This article argues for a more sophisticated connection between these diverse systems based on the fact that they are all complex self-organizing systems, operating far from thermodynamic equilibrium. As such, industrial and ecological systems have in common certain constraints and dynamic properties that move beyond the central metaphor of industrial ecology and could align these systems under a more comprehensive analytical framework. If incorporated at a fundamental level, the complex systems framework could add depth and sophistication to the field of industrial ecology.     

Mitochondrial glycosidic residues contribute to the interaction between ruthenium amine complexes and the calcium uniporter

The role of glycosidic residues in the inhibitory properties of ruthenium complexes on mitochondrial calcium uptake was determined in mitoplasts.Our results showed that the binding and inhibitory properties of ruthenium amine complexes were modified when mitoplasts were exposed to N-glycosidase F action, but calcium uptake was not altered. N-linked proteins of the mitochondrial inner membrane were identified. We detected an 18-kDa protein that binds labeled Ru₃₆₀ under control conditions, but failed to bind the inhibitor after deglycosilation. A relationship between this protein and the action of ruthenium amine inhibitors of the mitochondrial uniporter is proposed.