dbSWEET: An Integrated Resource for SWEET Superfamily to Understand,Analyze and Predict the Function of Sugar Transporters in Prokaryotes and Eukaryotes

SWEET (Sweet Will Eventually be Exported Transporter) proteins have been recently discovered and form one of the three major families of sugar transporters. Homologs of SWEET are found in both prokaryotes and eukaryotes. Bacterial SWEET homologs have three transmembrane segments forming a triple-helical bundle and the functional form is dimers. Eukaryotic SWEETs have seven transmembrane helical segments forming two triple-helical bundles with a linker helix. Members of SWEET homologs have been shown to be involved in several important physiological processes in plants. However, not much is known regarding the biological significance of SWEET homologs in prokaryotes and in mammals. We have collected more than 2000 SWEET homologs from both prokaryotes and eukaryotes. For each homolog, we have modeled three different conformational states representing outward open, inward open and occluded states. We have provided details regarding substrate-interacting residues and residues forming the selectivity filter for each SWEET homolog. Several search and analysis options are available. The users can generate a phylogenetic tree and structure-based sequence alignment for selected set of sequences. With no metazoan SWEETs functionally characterized, the features observed in the selectivity filter residues can be used to predict the potential substrates that are likely to be transported across the metazoan SWEETs. We believe that this database will help the researchers to design mutational experiments and simulation studies that will aid to advance our understanding of the physiological role of SWEET homologs. This database is freely available to the scientific community at http://bioinfo.iitk.ac.in/bioinfo/dbSWEET/Home.     

Assessing photosystem I and II distribution in leaves from C4 plants using confocal laser scanning microscopy

Images of chlorophyll fluorescence emitted at wavelengths above and below 700 nm were recorded from leaf sections of C₄ species using confocal laser scanning microscopy (LSM). We investigated species exhibiting both NAD-malic enzyme (NAD-ME) C₄ photosynthesis and NADP-malic enzyme (NADP-ME) C₄ photosynthesis. Comparing LSM fluorescence of leaf sections with flow-cytometrically determined fluorescence from individual chloroplasts revealed that LSM fluorescence was distorted by the optical properties of leaf sections. Leaf section fluorescence, when corrected by transmission data derived from light transmission images, agreed with flow cytometry data. The corrected LSM fluorescence yielded information on the distribution of the individual photosystems in the C₄ leaf sections: PSII concentrations in bundle sheath cells were elevated in NAD-ME species but diminished in most of the NADP-ME species investigated. The NADP-ME species, Arundinella hirta, however, showed normal PSII and increased PSI concentration in bundle sheath chloroplasts. Finally, a gradient of PSI was observed within the bundle sheath cells from Euphorbia maculata.     

3D-structure of human estrogenic 17beta-HSD1: binding with various steroids.

Human estrogenic dehydrogenase (17β-HSD1) catalyses the last step in the biosynthesis of the active estrogens that stimulate the proliferation of breast cancer cells. While the primary substrate for the enzyme is estrone, the enzyme has some activity for the non-estrogenic substrates. To better understand the structure–function relationships of 17β-HSD1 and to provide a better ground for the design of inhibitors, we have determined the crystal structures of 17β-HSD1 in complex with different steroids.

The structure of the complex of estradiol with the enzyme determined previously (Azzi et al., Nature Structural Biology 3, 665–668) showed that the narrow active site was highly complementary to the substrate. The substrate specificity is due to a combination of hydrogen bonding and hydrophobic interactions between the steroid and the enzyme binding pocket. We have now determined structures of 17β-HSD1 in complex with dihydrotestosterone and 20-OH-progesterone. In the case of the C19 androgen, several residues within the enzyme active site make some small adjustments to accommodate the increased bulk of the substrate. In addition, the C19 steroids bind in a slightly different position from estradiol with shifts in positions of up to 1.4 Å. The altered binding position avoids unfavorable steric interactions between Leu 149 and the C19 methyl group (Han et al., unpublished). The known kinetic parameters for these substrates can be rationalized in light of the structures presented. These results give evidence for the structural basis of steroid recognition by 17β-HSD1 and throw light on the design of new inhibitors for this pivotal steroid enzyme.     

Human apolipoprotein E N-terminal domain displacement of apolipophorin III from insect low density lipophorin creates a receptor-competent hybrid lipoprotein

The surface of Manduca sexta low density lipophorin (LDLp) particles was employed as a template to examine the relative lipid binding affinity of the 22 kDa receptor binding domain (residues 1–183) of human apolipoprotein E3 (apo E3). Isolated LDLp was incubated with exogenous apolipoprotein and, following re-isolation by density gradient ultracentrifugation, particle apolipoprotein content was determined. Incubation of recombinant human apo E3(1–183) with LDLp resulted in a saturable displacement of apolipophorin III (apo Lp-III) from the particle surface, creating a hybrid apo E3(1–183)-LDLp. Although subsequent incubation with excess exogenous apo Lp-III failed to reverse the process, human apolipoprotein A-I (apo A-I) effectively displaced apo E3(1–183) from the particle surface. We conclude that human apo E N-terminal domain possesses a higher intrinsic lipid binding affinity than apo Lp-III but has a lower affinity than human apo A-I. The apo E3(1–183)-LDLp hybrid was competent to bind to the low density lipoprotein receptor on cultured fibroblasts. The system described is useful for characterizing the relative lipid binding affinities of wild type and mutant exchangeable apolipoproteins and evaluation of their biological properties when associated with the surface of a spherical lipoprotein.     

新疆罂粟属高山罂粟组分类研究

我国有罂粟属植物12种,新疆有10种,其中6种属于高山罂粟组。对新疆高山罂粟组植物的花葶进行了解剖研究,并用扫描电镜观察了花粉形态,结果表明,花葶中维管束的数量及排列方式在各种间存在着差异,可以作为一个鉴定特征。花粉上的小刺密度在放大12000倍时,在有种间存在着明显差异,可分类提供微观佐证。     

Design,synthesis, and conformational studies of the hGM‐CSF derived peptide (13–27)–Gly–(75–87)

An analogue of the human granulocyte–macrophage colony‐stimulating factor (hGM‐CSF), hGM‐CSF(13–27)–Gly–(75–87) was synthesized by solid phase methodology. This analogue was designed to comprise helices A and C of the native growth factor, linked by a glycine bridge. Helices A and C form half of a four‐helix bundle motif in the crystal structure of the native factor and are involved in the interaction with α‐ and β‐chains of the heterodimeric receptor. A conformational analysis of the synthetic analogue by CD, two‐dimensional nmr spectroscopy, and molecular dynamics calculations is reported. The analogue is in a random structure in water and assumes a partially α‐helical conformation in a 1 : 1 trifluoroethanol/water mixture. The helix content in this medium is ∼ 70%. By 2D‐nmr spectroscopy, two helical segments were identified in the sequences corresponding to helices A and C. In addition to medium‐ and short‐range NOESY connectivities, a long‐range cross peak was found between the Cβ proton of Val¹⁶ and NH proton of His⁸⁷ (using the numbering of the native protein). Experimentally derived interproton distances were used as restraints in molecular dynamics calculations, utilizing the x‐ray coordinates as the initial structure. The final structure is characterized by two helical segments in close spatial proximity, connected by a loop region. This structure is similar to that of the corresponding domain in the x‐ray structure of the native growth factor in which helices A and C are oriented in an antiparallel fashion. The N‐terminal residues Gly–Pro of helix C are involved in an irregular turn connecting the two helical segments. As a consequence, helix C is appreciably shifted and slightly rotated with respect to helix A compared to the x‐ray structure of the native growth factor. These small differences in the topology of the two helices could explain the lower biological activity of this analogue with respect to that of the native growth factor. © 1999 John Wiley & Sons, Inc. Biopoly 50: 545–554, 1999     

High spatial resolution mass spectrometry imaging reveals the genetically programmed,developmental modification of the distribution of thylakoid membrane lipids among individual cells of maize leaf

Metabolism in plants is compartmentalized among different tissues, cells and subcellular organelles. Mass spectrometry imaging (MSI) with matrix‐assisted laser desorption ionization (MALDI) has recently advanced to allow for the visualization of metabolites at single‐cell resolution. Here we applied 5‐ and 10 μm high spatial resolution MALDI‐MSI to the asymmetric Kranz anatomy of Zea mays (maize) leaves to study the differential localization of two major anionic lipids in thylakoid membranes, sulfoquinovosyldiacylglycerols (SQDG) and phosphatidylglycerols (PG). The quantification and localization of SQDG and PG molecular species, among mesophyll (M) and bundle sheath (BS) cells, are compared across the leaf developmental gradient from four maize genotypes (the inbreds B73 and Mo17, and the reciprocal hybrids B73 × Mo17 and Mo17 × B73). SQDG species are uniformly distributed in both photosynthetic cell types, regardless of leaf development or genotype; however, PG shows photosynthetic cell‐specific differential localization depending on the genotype and the fatty acyl chain constituent. Overall, 16:1‐containing PGs primarily contribute to the thylakoid membranes of M cells, whereas BS chloroplasts are mostly composed of 16:0‐containing PGs. Furthermore, PG 32:0 shows genotype‐specific differences in cellular distribution, with preferential localization in BS cells for B73, but more uniform distribution between BS and M cells in Mo17. Maternal inheritance is exhibited within the hybrids, such that the localization of PG 32:0 in B73 × Mo17 is similar to the distribution in the B73 parental inbred, whereas that of Mo17 × B73 resembles the Mo17 parent. This study demonstrates the power of MALDI‐MSI to reveal unprecedented insights on metabolic outcomes in multicellular organisms at single‐cell resolution.     

上海三级甲等医院移动医疗App应用现状调查

目的 全面了解上海市三级甲等医院App运营情况,探索进一步完善微信运营的有效措施。方法 应用文本分析法以及深度访谈法,以上海市40家三级甲等医院为调查样本,对其App应用软件的开通率、患者使用率以及功能建设情况进行调查。结果 在全市40家三级甲等医院中,App软件开通率为35%;在91助手、应用宝、乐商店等下载平台上,瑞金医院下载量最高,其余下载量均较低;在功能设置情况方面,领取报告、医院导航等互动功能开设率达85%,医院介绍、科室介绍等静态信息发布功能设置率仅为15%。结论 移动App正在不断深化服务内涵,提供细节服务,并汲取多方资源优势,采取互助共赢的合作模式。然而仍需通过院内院外、线上线下合作的方式加大推广力度,并进一步挖掘多方资源合作潜力,进一步探索细节服务。     

Ultrastructure of Enteromyxum leei (Diamant, Lom, & Dyková, 1994) (Myxozoa), an Enteric Parasite Infecting Gilthead Sea Bream (Sparus aurata) and Sharpsnout Sea Bream (Diplodus puntazzo)

ABSTRACT. The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream ( Sparus aurata ) intestine and sharpsnout sea bream ( Diplodus puntazzo ) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant β-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum .     

A conserved element that stabilizes the group II intron active site

The internal loop at the base of domain 3 (D3) is one of the most conserved and catalytically important elements of a group II intron. However, the location and molecular nature of its tertiary interaction partners has remained unknown. By employing a combination of site-directed photo-cross-linking and nucleotide analog interference suppression (NAIS), we show that the domain 3 internal loop (D3IL) interacts with the epsilon-epsilon' duplex, which is an active-site element located near the 5'-splice site in D1. Our data also suggest that the D3IL may interact with the bulge of D5, which is a critical active site component. The results of this and other recent studies indicate that the D3IL participates in a complex network of tertiary interactions involving epsilon-epsilon', the bulge of D5 and J23, and that it helps to optimize active site architecture by supporting interactions among these catalytic motifs. Our results are consistent with the role of D3 as a catalytic effector that enhances intron reactivity through active site stabilization.