Crystal Structure of the Tetrameric Fibrinogen-like Recognition Domain of Fibrinogen C Domain Containing 1 (FIBCD1) Protein

The high resolution crystal structures of a recombinant fragment of the C-terminal fibrinogen-like recognition domain of FIBCD1, a vertebrate receptor that binds chitin, have been determined. The overall tetrameric structure shows similarity in structure and aggregation to the horseshoe crab innate immune protein tachylectin 5A. The high affinity ligand N-acetylmannosamine (ManNAc) binds in the S1 site, predominantly via the acetyl group with the oxygen and acetamide nitrogen hydrogen-bonded to the protein and the methyl group inserted into a hydrophobic pocket. The binding of the ManNAc pyranose ring differs markedly between the two independent subunits, but in all structures the binding of the N-acetyl group is conserved. In the native structure, a crystal contact results in one of the independent protomers binding the first GlcNAc of the Asn³⁴⁰ N-linked glycan on the other independent protomer. In the ligand-bound structure this GlcNAc is replaced by the higher affinity ligand ManNAc. In addition, a sulfate ion has been modeled into the electron density at a location similar to the S3 binding site in L-ficolin, whereas in the native structure an acetate ion has been placed in the S1 N-acetyl binding site, and a sulfate ion has been placed adjacent to this site. These ion binding sites are ideally placed to receive the N-acetyl and sulfate groups of sulfated GalNAc residues of glycosaminoglycans such as chondroitin and dermatan sulfate. Together, these structures give insight into important determinants of ligand selectivity, demonstrating versatility in recognition and binding while maintaining conservation in N-acetyl and calcium binding.     

Structural Basis for Multiple Sugar Recognition of Jacalin-related Human ZG16p Lectin

ZG16p is a soluble mammalian lectin, the first to be described with a Jacalin-related β-prism-fold. ZG16p has been reported to bind both to glycosaminoglycans and mannose. To determine the structural basis of the multiple sugar-binding properties, we conducted glycan microarray analyses of human ZG16p. We observed that ZG16p preferentially binds to α-mannose-terminating short glycans such as Ser/Thr-linked O-mannose, but not to high mannose-type N-glycans. Among sulfated glycosaminoglycan oligomers examined, chondroitin sulfate B and heparin oligosaccharides showed significant binding. Crystallographic studies of human ZG16p lectin in the presence of selected ligands revealed the mechanism of multiple sugar recognition. Manα1–3Man and Glcβ1–3Glc bound in different orientations: the nonreducing end of the former and the reducing end of the latter fitted in the canonical shallow mannose binding pocket. Solution NMR analysis using ¹⁵N-labeled ZG16p defined the heparin-binding region, which is on an adjacent flat surface of the protein. On-array competitive binding assays suggest that it is possible for ZG16p to bind simultaneously to both types of ligands. Recognition of a broad spectrum of ligands by ZG16p may account for the multiple functions of this lectin in the formation of zymogen granules via glycosaminoglycan binding, and in the recognition of pathogens in the digestive system through α-mannose-related recognition.     

Identification of Multifaceted Binding Modes for Pyrin and ASC Pyrin Domains Gives Insights into Pyrin Inflammasome Assembly

Inflammasomes are macromolecular complexes that mediate inflammatory and cell death responses to pathogens and cellular stress signals. Dysregulated inflammasome activation is associated with autoinflammatory syndromes and several common diseases. During inflammasome assembly, oligomerized cytosolic pattern recognition receptors recruit procaspase-1 and procaspase-8 via the adaptor protein ASC. Inflammasome assembly is mediated by pyrin domains (PYDs) and caspase recruitment domains, which are protein interaction domains of the death fold superfamily. However, the molecular details of their interactions are poorly understood. We have studied the interaction between ASC and pyrin PYDs that mediates ASC recruitment to the pyrin inflammasome, which is implicated in the pathogenesis of familial Mediterranean fever. We demonstrate that both the ASC and pyrin PYDs have multifaceted binding modes, involving three sites on pyrin PYD and two sites on ASC PYD. Molecular docking of pyrin-ASC PYD complexes showed that pyrin PYD can simultaneously interact with up to three ASC PYDs. Furthermore, ASC PYD can self-associate and interact with pyrin, consistent with previous reports that pyrin promotes ASC clustering to form a proinflammatory complex. Finally, the effects of familial Mediterranean fever-associated mutations, R42W and A89T, on structural and functional properties of pyrin PYD were investigated. The R42W mutation had a significant effect on structure and increased stability. Although the R42W mutant exhibited reduced interaction with ASC, it also bound less to the pyrin B-box domain responsible for autoinhibition and hence may be constitutively active. Our data give new insights into the binding modes of PYDs and inflammasome architecture.     

5,6-Dimethylxanthenone-4-acetic Acid (DMXAA) Activates Stimulator of Interferon Gene (STING)-dependent Innate Immune Pathways and Is Regulated by Mitochondrial Membrane Potential

The chemotherapeutic agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a potent inducer of type I IFNs and other cytokines. This ability is essential for its chemotherapeutic benefit in a mouse cancer model and suggests that it might also be useful as an antiviral agent. However, the mechanism underlying DMXAA-induced type I IFNs, including the host proteins involved, remains unclear. Recently, it was reported that the antioxidant N-acetylcysteine (NAC) decreased DMXAA-induced TNF-α and IL-6, suggesting that oxidative stress may play a role. The goal of this study was to identify host proteins involved in DMXAA-dependent signaling and determine how antioxidants modulate this response. We found that expression of IFN-β in response to DMXAA in mouse macrophages requires the mitochondrial and endoplasmic reticulum resident protein STING. Addition of the antioxidant diphenylene iodonium (DPI) diminished DMXAA-induced IFN-β, but this decrease was independent of both the NADPH oxidase, Nox2, and de novo generation of reactive oxygen species. Additionally, IFN-β up-regulation by DMXAA was inhibited by agents that target the mitochondrial electron transport chain and, conversely, loss of mitochondrial membrane potential correlated with diminished innate immune signaling in response to DMXAA. Up-regulation of Ifnb1 gene expression mediated by cyclic dinucleotides was also impaired by DPI, whereas up-regulation of Ifnb1 mRNA due to cytosolic double-stranded DNA was not. Although both stimuli signal through STING, cyclic dinucleotides interact directly with STING, suggesting that recognition of DMXAA by STING may also be mediated by direct interaction.     

飞行状态下四种菊头蝠回声定位声波的小波包识别方法

研究了飞行状态下的四种菊头蝠回声定位声波的识别方法.通过小波包分解得到各个频带能量作为识一别特征向量,用主成分分析法优化特征空间.提取少数几个主成分,这些主成分彼此不相关,符合特征优化的要求,以主成分向量作为BP神经网络的输入对蝙蝠的种类进行识别.个体识别正确率达到了80%以上,表明基于小渡包分解和神经网络识别的方法对蝙蝠回声定位声波进行识别是可行的.     

分支位点在真核基因受体位点识别中的作用

真核基因受体位点识别是剪接位点识别的一部分,也是基因识别中的重要环节,一直受到研究人员的关注。已有的研究结果显示受体位点的识别与分支位点有关,然而关于分支位点和受体位点识别的关系问题,目前还无人将其作为专门的问题予以深入研究。从受体位点识别出发,选取不同的受体位点序列长度,以神经网络为识别工具,对分支位点在受体位点识别中的作用做了深入研究和分析。实验结果表明,受体位点序列的特征信息集中在分支位点一例,因此分支位点在受体位点识别中具有重要作用。研究结果为受体位点识别问题中序列特征提取提供了依据。     

Studies on Image Automated Analysis and Recognition of Plant Chromosome

A plant chromosome image analysis CHROM. HUK software system has been developed in the light of the theory of image analysis and recognition and applied in karyotype automated analysis of Xizang wild barley (Hordeum agriocrithon Aberg var. nigrum) and Cupressus gigantea Cheng et L. K. Fu. The main features of automated analysis include the pre-processing of chromosome image, determinating peak-valley threshold of chromosome, separation of overlapping chromosome, evaluation of centre line of chromosome,limit erotion recognition of position of centromere and second constric, extraction of characterictic parameters of chromosome and karyotype analysis. The vast amount of data obtained could be stored, operated and used for further statistical analysis. According to the estimation in the 95% confidence interval and the tree type sort, the chromosome were paired and sorted. In the meantime, a karyogram and an idiogram of karyotype were generated automatically through computerization.     

Macrocyclic zinc(II) complexes for selective recognition of nucleobases in single- and double-stranded polynucleotides

 As an extension of our earlier discoveries that Zn^II-cyclen complex (1) (cyclen=1,4,7,10-tetraazacyclododecane) and Zn^II-acridine-pendant cyclen complex Zn^II-N-(9-acridin)ylmethyl-cyclen (3) are the first compounds to selectively recognize thymidine and uridine nucleosides in aqueous solution at physiological pH, the interaction of these and a relevant complex, bis(Zn^II-cyclen) (7), has been investigated with a series of polynucleotides, single-stranded poly(U) and poly(G), and double-stranded poly(A)·poly(U), poly(dA)·poly(dT) and poly(dG)·poly(dC). These Zn^II-cyclen complexes interact with the imide-containing nucleobases in the single-stranded poly(U), unperturbed by the presence of the anionic phosphodiester backbone. The affinity constant of 1 for each N(3)-deprotonated uracil base in poly(U) is determined to be log K= 5.1 by a kinetic measurement, which is almost the same as log K=5.2 for the interaction of 1 with uridine. Thus, they disrupt the A-U (or A-T) hydrogen bonds to unzip the duplex of poly(A)·poly(U) or poly(dA)·poly(dT), as demonstrated by lowering of the melting temperatures (T _m) of poly(A)·poly(U) and poly(dA)·poly(dT) in 5 mM Tris-HCl buffer (pH 7.6, 10 mM NaCl) with increase in their concentrations. The order of the denaturing efficiency is well correlated with that of the 1 : 1 affinity constants for each complex with uracil or thymine;7>3>1. The comparison of circular dichroism (CD) spectra for poly(A)·poly(U), poly(A), and poly(U) in the presence of 3 has revealed a structural change from poly(A)·poly(U) to two single strands, poly(A) and poly(U), caused by 3 binding exclusively to uracils in poly(U). On the other hand, the acridine-pendant cyclen complex 3, which earlier was found to associate with guanine by the Zn^II coordinating with guanine N(7), in addition to the π-π stacking, interacts with guanine in the double helix of poly(dG)·poly(dC) from outside and stabilized the double-stranded structure, as indicated by higher T _m. Received: 31 December 1997 / Accepted: 23 February 1998