Mechanism of mechanical regulated Notch activation and structural bases of Notch NRR related T-lineage acute lymphoblastic leukemia(T-ALL)

Notch proteins are transmembrane receptors which can transduce signals between cells.Upon binding to their ligands on the neighboring cells,notch receptors can be activated and undergo conformational changes which enable their proteolysis by ADAM-family of metalloproteases[1].The cleavage site of notch protein located on its hetrodimerizaton domain（HD）of the negative regulatory region（NRR）proximal to the N-terminal of the transmembrane helix.Recent crystal structures on several notch proteins[2-4]indicated that a series of three Lin12/Notch repeats（LNRs）wrap around the HD and bury the cleavage site to prevent it from proteolysis at the normal conditions without ligand binding.Studies indicated that notch/ligand binding may al-

机械力诱导MHC-Ⅰ构象变化增强TCR抗原识别及T细胞活化

CD8+T细胞主要通过T细胞表面受体(T cell recep tor,TCR)识别并与Ⅰ型主要组织性复合物提呈的抗原(pMHC-Ⅰ)相互作用[1]。TCR对刺激型抗原的识别在CD8+T细胞毒性和适应性免疫中发挥着关键作用。许多证据表明机械力可以延长TCR与刺激性pMHC作用的键合时间(bond lifetime)形成抗原特异性逆锁键(catch bond)[2],并且这种逆锁键对抗原识别非常重要。然而,机械力调控TCR抗原识别的具体结构机制仍不清楚。通过分子动力学模拟、单分子生物膜力学探针、磁镊、T细胞活化实验和动物模型对此问题展开了系统的研究[4]。发现作用在TCR-pMHC-Ⅰ复合体上的拉力可以作用在TCR-pMHC-Ⅰ复合体上的拉力可以打破MHC-I分子内部α1-α2和β2结构域间的相互作用,导致α1-α2结构域旋转并发生构象变化。力诱导的MHC-I构象变化可以进一步别构地调节TCR与刺激性抗原肽及α1-α2结构域的构象及相互作用,诱导产生新的氢键,增强TCR-pMHC-Ⅰ之间的键合时间,但并不能增强TCR与抑制性pMHC-Ⅰ之间的作用。当用点突变阻断这些新形成的氢键,或者α1-α2和β2结构域被二硫键锁住时,最佳力诱导的TCR-pMHC-Ⅰ作用的键合时间明显缩短并且T细胞的活化受到抑制。另外,在人TCR和HLA-A2相互作用中发现了类似机制,并且与肿瘤相关的HLA-A2点突变[3]可以通过限制HLA-A2α1--α2和β2结构域之间的构象打开减弱TCR对肿瘤抗原的识别及T细胞的功能。研究结果表明,机械力诱导的MHC-I构象变化对TCR抗原识别和T细胞活化非常重要,进一步地阐明了机械力调控TCR抗原识别机制,为临床肿瘤的免疫治疗和药物设计提供了新思路和新靶点。

Mechanosensing via Immunereceptors

The immune response is orchestrated by a variety of immune cells,the function of which then is determined by the collective signals from different immunoreceptors.Recent studies have highlighted the presence of mechanical force on these receptor-ligand pairs and its important role in regulating antigen recognition/discrimination and function.In this perspective,we use the T cell receptor as an example to review the current understanding of the mechanosensing properties of immunoreceptors.We discuss the types of forces that immunoreceptors may encounter,the effects on ligand recognition,conformational changes and mechanosensing mechanisms,as well as the consequences in downstream signal transduction and function.

Liquid-liquid phase separation in biology: mechanisms,physiological functions and human diseases

Cells are compartmentalized by numerous membrane-enclosed organelles and membraneless compartments to ensure that a wide variety of cellular activities occur in a spatially and temporally controlled manner. The molecular mechanisms underlying the dynamics of membrane-bound organelles, such as their fusion and fission, vesicle-mediated trafficking and membrane contactmediated inter-organelle interactions, have been extensively characterized. However, the molecular details of the assembly and functions of membraneless compartments remain elusive. Mounting evidence has emerged recently that a large number of membraneless compartments, collectively called biomacromolecular condensates, are assembled via liquid-liquid phase separation(LLPS). Phase-separated condensates participate in various biological activities, including higher-order chromatin organization,gene expression, triage of misfolded or unwanted proteins for autophagic degradation, assembly of signaling clusters and actin-and microtubule-based cytoskeletal networks, asymmetric segregations of cell fate determinants and formation of pre-and post-synaptic density signaling assemblies. Biomacromolecular condensates can transition into different material states such as gel-like structures and solid aggregates. The material properties of condensates are crucial for fulfilment of their distinct functions, such as biochemical reaction centers, signaling hubs and supporting architectures. Cells have evolved multiple mechanisms to ensure that biomacromolecular condensates are assembled and disassembled in a tightly controlled manner. Aberrant phase separation and transition are causatively associated with a variety of human diseases such as neurodegenerative diseases and cancers. This review summarizes recent major progress in elucidating the roles of LLPS in various biological pathways and diseases.

Thiabendazole inhibits ubiquinone reduction activity of mitochondrial respiratory complex Ⅱ via a water molecule mediated binding feature

The mitochondrial respiratory complex Ⅱ or succinate:ubiquinone oxidoreductase(SQR)is a key membrane complex in both the tricarboxylic acid cycle and aerobic respiration.Five disinfectant compounds were investigated with their potent inhibition effects on the ubiquinone reduction activity of the porcine mitochondrial SQR by enzymatic assay and crystallography.Crystal structure of the SQR bound with thiabendazole(TBZ)reveals a different inhibitor-binding feature at the ubiquinone binding site where a water molecule plays an important role.The obvious inhibitory effect of TBZ based on the biochemical data(IC50~100μmol/L)and the significant structure-based binding affinity calculation(~94μmol/L)draw the suspicion of using TBZ as a good disinfectant compound for nematode infections treatment and fruit storage.

Mechanical unfolding of a β-barrel membrane protein by single-molecule force spectroscopy

Dear Editor.Transmembrane proteins with β-barrel topology are mainly found in the outer membranes(OMs)of Gram-negative bacteria,mitochondria and chloroplasts(Wimley,2003).These proteins usually contain even numbers of β-strands,ranging from 8-36.To achieve an overall cylindrical topology,the polypeptide chain of a β-barrel OMP must fold to form a series of anti-parallel β-strands with each β-strand hydrogen-bonding to its neighboring strands(Otzen and Andersen,2013).The folding and insertion of a β-barrel OMP in vivo requires an evolutionarily conserved multiprotein complex termedβ-barrel assembly machinery(BAM)complex(Noinaj et al.,2015).