A novel anterograde trafficking signal present in the N-terminal extracellular domain of ionotropic glutamate receptors

Trafficking of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors to and from the postsynaptic membrane plays an important role in regulating transmission at excitatory synapses. AMPA receptor subunits contain a large extracellular N-terminal domain that is important for receptor assembly (). To further investigate the determinants of receptor assembly and surface expression, we have epitope-tagged the N-terminal domain of the AMPA receptor subunit, GluR1, and expressed it in human embryonic kidney 293 cells and hippocampal neurons. Full-length GluR1 was readily detected on the cell surface in both cell types. However, surface expression was profoundly decreased by deletion or replacement of nine amino acids in the extreme N terminus. Immunoprecipitation experiments demonstrated that the mutant GluR1 in which this sequence was deleted still interacts with GluR2, suggesting that mutant GluR1 is capable of at least partial assembly into heteromeric structures. The mutant forms of GluR1 co-localize with an endoplasmic reticulum marker suggesting that they are retained in this structure. These results suggest a specific function of a short sequence present in the N-terminal domain in controlling anterograde trafficking of ionotropic glutamate receptors.     

Development of a set of expression vectors in Hansenula polymorpha

Four expression vectors based on formate dehydrogenase promoter (FMDp) and methanol oxidase promoter (MOXp) from Hansenula polymorpha were developed to express heterologous genes in Hansenula polymorpha. A secretion signal sequence of the mating factor-alpha from Saccharomyces cerevisiae was inserted in the secretory expression plasmids for efficient secretion. A modified green fluorescent protein (mGFP5) was used as the marker of expression for the first time in H. polymorpha NCYC495 (leu 1.1) to determine the expression ability of these plasmids. The mGFP5 thus expressed retained its biochemical and physiological properties, such as accumulation inside cells and efficient secretion into the culture media. These results indicated that the four integrative vectors are useful expression systems which could be directly applied for production of heterologous proteins of interests in H. polymorpha.     

A Novel Mucosal Vaccine Against Foot-and-Mouth Disease Virus Induces Protection in Mice and Swine

Epitopes of a foot-and-mouth disease virus (FMDV) capsid protein VP1 complex and a chimera of 6×His-tagged cholera toxin B subunit (hCTB) were expressed in Hansenula polymorpha and used together as a mucosal vaccine. Antibody and cytokine responses to VP1–hCTB vaccine and protection against FMDV were evaluated by ELISA and a virus challenge test in mice, respectively. VP1–hCTB directly enhanced the expression of interleukin-5 (IL-5) both in serum and supernatants of cultured spleen cells. After challenging suckling mice with 10⁵ FMDV (=50% lethal dosage per mouse) a greater protection was seen after intraperitoneal and intranasal vaccinations than after oral vaccination. In swine immunized with VP1–hCTB, immune responses were achieved after three administrations, and the vaccine protected swine (80%) when challenged with 10^6.5 FMDV (=50% infectious dosage per swine). These results demonstrated the possibility of using CTB as a mucosal adjuvant to elicit protective immune responses against FMDV. Houhui Song, Zhiliang Wang and Dongxia Zheng contributed equally to this work.     

Rab8 Interacts with Distinct Motifs in α2B- and β2-Adrenergic Receptors and Differentially Modulates Their Transport

The molecular mechanism underlying the post-Golgi transport of G protein-coupled receptors (GPCRs) remains poorly understood. Here we determine the role of Rab8 GTPase, which modulates vesicular protein transport between the trans-Golgi network (TGN) and the plasma membrane, in the cell surface targeting of α_2B- and β₂-adrenergic receptors (AR). Transient expression of GDP- and GTP-bound Rab8 mutants and short hairpin RNA-mediated knockdown of Rab8 more potently inhibited the cell surface expression of α_2B-AR than β₂-AR. The GDP-bound Rab8(T22N) mutant attenuated ERK1/2 activation by α_2B-AR, but not β₂-AR, and arrested α_2B-AR in the TGN compartment. Co-immunoprecipitation revealed that both α_2B-AR and β₂-AR physically interacted with Rab8 and glutathione S-transferase fusion protein pulldown assays demonstrated that Rab8 interacted with the C termini of both receptors. Interestingly, mutation of the highly conserved membrane-proximal C terminus dileucine motif selectively blocked β₂-AR interaction with Rab8, whereas mutation of residues Val⁴³¹-Phe⁴³²-Asn⁴³³-Gln⁴³⁴, Pro⁴⁴⁷-Trp⁴⁴⁸, Gln⁴⁵⁰-Thr⁴⁵¹, and Trp⁴⁵³ in the C terminus impaired α_2B-AR interaction with Rab8. Furthermore, transport inhibition by Rab8(T22N) of a chimeric β₂-AR carrying the α_2B-AR C terminus was similar to α_2B-AR. These data provide strong evidence indicating that Rab8 GTPase interacts with distinct motifs in the C termini of α_2B-AR and β₂-AR and differentially modulates their traffic from the TGN to the cell surface.     

基于光激活定位显微镜的膜蛋白鉴定技术

病原菌膜蛋白的原位标记和定位追踪是一项非常繁琐的工作。为了建立一种可以用于快速鉴定膜蛋白、且分辨率达到纳米级别的膜蛋白荧光定位技术,将结核分枝杆菌外膜蛋白OmpA与具有光敏活性的蛋白mEos2m在无致病性的耻垢分枝杆菌中进行融合表达。重组菌固定在载玻片上后,利用405 nm激光激活mEos2m。利用普通荧光体视显微镜、正置荧光显微镜和超分辨率光激活定位显微镜观察OmpA-mEos2m,分析融合蛋白在细菌内的分布情况,并捕获光激活蛋白在细胞膜上释放的光子信号。通过超分辨率光激活定位显微镜,发现OmpA-mEos2m融合蛋白在细胞膜上呈"带"状环绕分布,这是观察到膜蛋白在细胞膜上定位的最直接证据。mEos2m与OmpA融合表达后,并不改变OmpA的膜蛋白属性和定位特征。因此可以将mEos2m用于其他非多聚体膜蛋白的融合和定位研究。可以应用非致病性的耻垢分枝杆菌作为模型,采用高分辨率活菌成像技术,研究致病性的结核分枝杆菌蛋白结构、定位和功能。这是目前为止国内采用光激活定位显微成像技术研究膜蛋白的首次报道。     

结核分枝杆菌诱导IFN-β产生在免疫调控中的作用

结核分枝杆菌是导致结核病的病原体,也是影响全球数百万人健康的病原体之一。机体中多种模式识别受体(pattern recognition receptor,PRR)可识别入侵的结核分枝杆菌,如DNA和RNA传感器,从而激活天然免疫系统并诱导干扰素-β(interferon-β, IFN-β)产生。虽然IFN-β是先天抗病毒应答的主要效应因子,但其在结核分枝杆菌感染中的作用仍具有争议。结核分枝杆菌感染诱导的IFN-β产生可以促进细菌生长,并增强细菌在宿主中的存活率,但用IFN-β处理细胞后再感染结核分枝杆菌,则可增强抗菌作用,保护宿主。因此,本综述将重点关注可识别结核分枝杆菌并诱导的IFN-β产生的PRR及其下游信号通路,并着重探讨IFN-β在介导结核分枝杆菌调控免疫功能中的作用,尤其是IFN-β与IL-1β之间的相互抑制性调节,旨在为进一步揭示结核分枝杆菌致病机制及结核病治疗药物研发提供新思路。     

Actinin-associated LIM Protein: Identification of a Domain Interaction between PDZ and Spectrin-like Repeat Motifs

PDZ motifs are protein–protein interaction domains that often bind to COOH-terminal peptide sequences. The two PDZ proteins characterized in skeletal muscle, syntrophin and neuronal nitric oxide synthase, occur in the dystrophin complex, suggesting a role for PDZ proteins in muscular dystrophy. Here, we identify actinin-associated LIM protein (ALP), a novel protein in skeletal muscle that contains an NH₂-terminal PDZ domain and a COOH-terminal LIM motif. ALP is expressed at high levels only in differentiated skeletal muscle, while an alternatively spliced form occurs at low levels in the heart. ALP is not a component of the dystrophin complex, but occurs in association with α-actinin-2 at the Z lines of myofibers. Biochemical and yeast two-hybrid analyses demonstrate that the PDZ domain of ALP binds to the spectrin-like motifs of α-actinin-2, defining a new mode for PDZ domain interactions. Fine genetic mapping studies demonstrate that ALP occurs on chromosome 4q35, near the heterochromatic locus that is mutated in fascioscapulohumeral muscular dystrophy.     

Signaling from synapse to nucleus: the logic behind the mechanisms

Signaling from synapse to nucleus is vital for activity-dependent control of neuronal gene expression and represents a sophisticated form of neural computation. The nature of specific signal initiators, nuclear translocators and effectors has become increasingly clear, and supports the idea that the nucleus is able to make sense of a surprising amount of fast synaptic information through intricate biochemical mechanisms. Information transfer to the nucleus can be conveyed by physical translocation of messengers at various stages within the multiple signal transduction cascades that are set in motion by a Ca(2+) rise near the surface membrane. The key role of synapse-to-nucleus signaling in circadian rhythms, long-term memory, and neuronal survival sheds light on the logical underpinning of these signaling mechanisms.