Activation of the ILT7 receptor and plasmacytoid dendritic cell responses are governed by structurally-distinct BST2 determinants.

Type I interferons (IFN-I) are key innate immune effectors predominantly produced by activated plasmacytoid dendritic cells (pDCs). By modulating immune responses at their foundation, IFNs can widely reshape immunity to control infectious diseases and malignancies. Nevertheless, their biological activities can also be detrimental to surrounding healthy cells, as prolonged IFN-I signaling is associated with excessive inflammation and immune dysfunction. The interaction of the human pDC receptor immunoglobulin-like transcript 7 (ILT7) with its IFN-I-regulated ligand, bone marrow stromal cell antigen 2 (BST2) plays a key role in controlling the IFN-I amounts produced by pDCs in response to Toll-like receptor (TLR) activation. However, the structural determinants and molecular features of BST2 that govern ILT7 engagement and activation are largely undefined. Using two functional assays to measure BST2-stimulated ILT7 activation as well as biophysical studies, here we identified two structurally-distinct regions of the BST2 ectodomain that play divergent roles during ILT7 activation. We found that although the coiled-coil region contains a newly defined ILT7-binding surface, the N-terminal region appears to suppress ILT7 activation. We further show that a stable BST2 homodimer binds to ILT7, but post-binding events associated with the unique BST2 coiled-coil plasticity are required to trigger receptor signaling. Hence, BST2 with an unstable or a rigid coiled-coil fails to activate ILT7, whereas substitutions in its N-terminal region enhance activation. Importantly, the biological relevance of these newly defined domains of BST2 is underscored by the identification of substitutions having opposing potentials to activate ILT7 in pathological malignant conditions.

Three-dimensional chemical mapping by EFTEM-TomoJ including improvement of SNR by PCA and ART reconstruction of volume by noise suppression.

Electron tomography is becoming one of the most used methods for structural analysis at nanometric scale in biological and materials sciences. Combined with chemical mapping, it provides qualitative and semiquantitative information on the distribution of chemical elements on a given sample. Due to the current difficulties in obtaining three-dimensional (3D) maps by energy-filtered transmission electron microscopy (EFTEM), the use of 3D chemical mapping has not been widely adopted by the electron microscopy community. The lack of specialized software further complicates the issue, especially in the case of data with a low signal-to-noise ratio (SNR). Moreover, data interpretation is rendered difficult by the absence of efficient segmentation tools. Thus, specialized software for the computation of 3D maps by EFTEM needs to include optimized methods for image series alignment, algorithms to improve SNR, different background subtraction models, and methods to facilitate map segmentation. Here we present a software package (EFTEM-TomoJ, which can be downloaded from http://u759.curie.fr/fr/download/softwares/EFTEM-TomoJ), specifically dedicated to computation of EFTEM 3D chemical maps including noise filtering by image reconstitution based on multivariate statistical analysis. We also present an algorithm named BgART (for background removing algebraic reconstruction technique) allowing the discrimination between background and signal and improving the reconstructed volume in an iterative way.

La tétherine, dernière amarre du VIH.

Tetherin is an unusual surface glycoprotein that employs an N-terminal and a C-terminal region to anchor the protein into membranes. Structural analyses revealed an elongated structure for the ectodomain that is probably oriented parallel to cellular membranes. Expression of tetherin can be induced by interferon in selected cell types, which leads to the restriction of HIV-1 replication in the absence of the viral antagonist Vpu. This review focuses on recent progress on the understanding of the molecular mechanisms of tetherin function during HIV and other enveloped virus budding processes. We discuss the role of diverse viral antagonists in tetherin down regulation and place the structural information on the ectodomain into the context of tetherin's ability to physically link virions such as HIV-1 to the plasma membrane after completion of budding.