The structural basis for the association of eukaryotic and prokaryotic protein receptors and their triple‐helical collagen ligand remains poorly understood. Here, we present the crystal structures of a high affinity subsegment of the Staphylococcus aureus collagen‐binding CNA as an apo‐protein and in complex with a synthetic collagen‐like triple helical peptide. The apo‐protein structure is composed of two subdomains (N1 and N2), each adopting a variant IgG‐fold, and a long linker that connects N1 and N2. The structure is stabilized by hydrophobic inter‐domain interactions and by the N2 C‐terminal extension that complements a β‐sheet on N1. In the ligand complex, the collagen‐like peptide penetrates through a spherical hole formed by the two subdomains and the N1–N2 linker. Based on these two structures we propose a dynamic, multistep binding model, called the ‘Collagen Hug’ that is uniquely designed to allow multidomain collagen binding proteins to bind their extended rope‐like ligand.

Through a proteomic analysis of ER–PM junctions, Zhou and colleagues and Wang and colleagues discover that the transmembrane protein STIMATE is a positive regulator of STIM localization and function, thereby stimulating Ca2+ influx. Specialized junctional sites that connect the plasma membrane (PM) and endoplasmic reticulum (ER) play critical roles in controlling lipid metabolism and Ca2+ signalling1,2,3,4. Store-operated Ca2+ entry mediated by dynamic STIM1–ORAI1 coupling represents a classical molecular event occurring at ER–PM junctions, but the protein composition and how previously unrecognized protein regulators facilitate this process remain ill-defined. Using a combination of spatially restricted biotin labelling in situ coupled with mass spectrometry5,6 and a secondary screen based on bimolecular fluorescence complementation7, we mapped the proteome of intact ER–PM junctions in living cells without disrupting their architectural integrity. Our approaches led to the discovery of an ER-resident multi-transmembrane protein that we call STIMATE (STIM-activating enhancer, encoded by TMEM110) as a positive regulator of Ca2+ influx in vertebrates. STIMATE physically interacts with STIM1 to promote STIM1 conformational switch. Genetic depletion of STIMATE substantially reduces STIM1 puncta formation at ER–PM junctions and suppresses the Ca2+–NFAT signalling. Our findings enable further genetic studies to elucidate the function of STIMATE in normal physiology and disease, and set the stage to uncover more uncharted functions of hitherto underexplored ER–PM junctions.

Store-operated Ca²⁺ entry mediated by STIM1 and ORAI1 constitutes one of the major Ca²⁺ entry routes in mammalian cells. The molecular choreography of STIM1–ORAI1 coupling is initiated by endoplasmic reticulum (ER) Ca²⁺ store depletion with subsequent oligomerization of the STIM1 ER-luminal domain, followed by its redistribution towards the plasma membrane to gate ORAI1 channels. The mechanistic underpinnings of this inside-out Ca²⁺ signalling were largely undefined. By taking advantage of a unique gain-of-function mutation within the STIM1 transmembrane domain (STIM1-TM), here we show that local rearrangement, rather than alteration in the oligomeric state of STIM1-TM, prompts conformational changes in the cytosolic juxtamembrane coiled-coil region. Importantly, we further identify critical residues within the cytoplasmic domain of STIM1 (STIM1-CT) that entail autoinhibition. On the basis of these findings, we propose a model in which STIM1-TM reorganization switches STIM1-CT into an extended conformation, thereby projecting the ORAI-activating domain to gate ORAI1 channels.

The management of CNS tumors is limited by the blood-brain barrier (BBB), a vascular interface that restricts the passage of most molecules from the blood into the brain. Here we show that phage particles targeted with certain ligand motifs selected in vivo from a combinatorial peptide library can cross the BBB under normal and pathological conditions. Specifically, we demonstrated that phage clones displaying an iron-mimic peptide were able to target a protein complex of transferrin and transferrin receptor (TfR) through a non-canonical allosteric binding mechanism and that this functional protein complex mediated transport of the corresponding viral particles into the normal mouse brain. We also showed that, in an orthotopic mouse model of human glioblastoma, a combination of TfR overexpression plus extended vascular permeability and ligand retention resulted in remarkable brain tumor targeting of chimeric adeno-associated virus/phage particles displaying the iron-mimic peptide and carrying a gene of interest. As a proof of concept, we delivered the HSV thymidine kinase gene for molecular-genetic imaging and targeted therapy of intracranial xenografted tumors. Finally, we established that these experimental findings might be clinically relevant by determining through human tissue microarrays that many primary astrocytic tumors strongly express TfR. Together, our combinatorial selection system and results may provide a translational avenue for the targeted detection and treatment of brain tumors.