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SummaryEndoglin (ENG)/CD105 is an essential endothelial cell co-receptor of the transforming growth factor β (TGF-β) superfamily, mutated in hereditary hemorrhagic telangiectasia type 1 (HHT1) and involved in tumor angiogenesis and preeclampsia. Here, we present crystal structures of the ectodomain of human ENG and its complex with the ligand bone morphogenetic protein 9 (BMP9). BMP9 interacts with a hydrophobic surface of the N-terminal orphan domain of ENG, which adopts a new duplicated fold generated by circular permutation. The interface involves residues mutated in HHT1 and overlaps with the epitope of tumor-suppressing anti-ENG monoclonal TRC105. The structure of the C-terminal zona pellucida module suggests how two copies of ENG embrace homodimeric BMP9, whose binding is compatible with ligand recognition by type I but not type II receptors. These findings shed light on the molecular basis of the BMP signaling cascade, with implications for future therapeutic interventions in this fundamental pathway.

Uromodulin (UMOD)/Tamm-Horsfall protein, the most abundant human urinary protein, plays a key role in chronic kidney diseases and is a promising therapeutic target for hypertension. Via its bipartite zona pellucida module (ZP-N/ZP-C), UMOD forms extracellular filaments that regulate kidney electrolyte balance and innate immunity, as well as protect against renal stones. Moreover, saltdependent aggregation of UMOD filaments in the urine generates a soluble molecular net that captures uropathogenic bacteria and facilitates their clearance. Despite the functional importance of its homopolymers, no structural information is available on UMOD and how it self-assembles into filaments. Here, we report the crystal structures of polymerization regions of human UMOD and mouse ZP2, an essential sperm receptor protein that is structurally related to UMOD but forms heteropolymers. The structure of UMOD reveals that an extensive hydrophobic interface mediates ZP-N domain homodimerization. This arrangement is required for filament formation and is directed by an ordered ZP-N/ZP-C linker that is not observed in ZP2 but is conserved in the sequence of deafness/Crohn's disease-associated homopolymeric glycoproteins α-tectorin (TECTA) and glycoprotein 2 (GP2). Our data provide an example of how interdomain linker plasticity can modulate the function of structurally similar multidomain proteins. Moreover, the architecture of UMOD rationalizes numerous pathogenic mutations in both UMOD and TECTA genes.uromodulin | ZP2 | polymerization | zona pellucida domain | X-ray crystallography U romodulin (UMOD) is expressed in the thick ascending limb of Henle's loop as a GPI membrane-anchored precursor that consists of three EGF-like domains, a domain of unknown function (D8C), and a zona pellucida (ZP) module (1, 2) (Fig. 1A, Top). The latter, containing Ig-like domains ZP-N and ZP-C (3-5), is found in other medically important human glycoproteins linked to infertility (egg coat components ZP1-ZP4), nonsyndromic deafness [inner ear α-and β-tectorin (TECTA/B)], Crohn's disease [glycoprotein 2 (GP2)], and cancer [TGF-β coreceptors betaglycan (BG) and endoglin (ENG)] (6, 7). Upon processing by Ser protease hepsin (8) at a consensus cleavage site (CCS) C-terminal to the ZP module (9), UMOD sheds a C-terminal propeptide (CTP) that contains a polymerization-blocking external hydrophobic patch (EHP), exposing an internal hydrophobic patch (IHP). This event triggers homopolymerization into filaments that are excreted into the urine (4, 10), where UMOD performs a plethora of biological functions, including protection against urinary tract infections, prevention of kidney stones, and activation of innate immunity (1,2,11,12).Although UMOD activity is strictly linked to its supramolecular state (2), the mechanism of ZP module-dependent assembly remains unclear. Mass spectroscopy (MS) analysis of ZP-C disulfide linkages suggests that there are two types of ZP modules with different structures (13). Type II contains 10 conserved Cys (C 1-7,a,b,8 ) and bo...

ID29 is an ESRF undulator beamline with a routinely accessible energy range of between 20.0 keV and 6.0 keV (= 0.62 Å to 2.07 Å) dedicated to the use of anomalous dispersion techniques in macromolecular crystallography. Since the beamline was first commissioned in 2001, ID29 has, in order to provide an improved service to both its academic and proprietary users, been the subject of almost continuous upgrade and refurbishment. It is now also the home to the ESRF Cryobench facility, ID29S. Here, the current status of the beamline is described and plans for its future are briefly outlined.