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Variant rs351855-G/A is a commonly occurring single-nucleotide polymorphism of coding regions in exon 9 of the fibroblast growth factor receptor FGFR4 (CD334) gene (c.1162G>A). It results in an amino-acid change at codon 388 from glycine to arginine (p.Gly388Arg) in the transmembrane domain of the receptor. Despite compelling genetic evidence for the association of this common variant with cancers of the bone (1), breast (2), colon (3), prostate (4,5), skin (6), lung (7,8), head and neck (9), as well as soft-tissue sarcomas and non-Hodgkin lymphoma, the underlying biological mechanism has remained elusive. Here we show that substitution of the conserved glycine 388 residue to a charged arginine residue alters the transmembrane spanning segment and exposes a membrane-proximal cytoplasmic signal transducer and activator of transcription 3 (STAT3) binding site [Y.sup.390]-(P)XXQ (393). We demonstrate that such membrane-proximal STAT3 binding motifs in the germline of type I membrane receptors enhance STAT3 tyrosine phosphorylation by recruiting STAT3 proteins to the inner cell membrane. Remarkably, such germline variants frequently co-localize with somatic mutations in the Catalogue of Somatic Mutations in Cancer (COSMIC) database. Using Fgfr4 single nucleotide polymorphism knock-in mice and transgenic mouse models for breast and lung cancers, we validate the enhanced STAT3 signalling induced by the FGFR4 Arg388-variant in vivo. Thus, our findings elucidate the molecular mechanism behind the genetic association of rs351855 with accelerated cancer progression and suggest that germline variants of cell-surface molecules that recruit STAT3 to the inner cell membrane are a significant risk for cancer prognosis and disease progression., We previously reported that the FGFR4 Arg388 allele (rs351855-A) located in exon 9 of the FGFR4 gene (Extended Data Fig. 1a) is associated with cancer progression and poor prognosis (6,7,9,10). [...]

Bile acids are synthesized from cholesterol in hepatocytes and secreted through the biliary tract into the small intestine, where they aid in absorption of lipids and fat-soluble vitamins. Through a process known as enterohepatic recirculation, more than 90% of secreted bile acids are then retrieved from the intestine and returned to the liver for resecretion (1). In humans, there are two [Na.sup.+]-dependent bile acid transporters involved in enterohepatic recirculation, the [Na.sup.+]-taurocholate co-transporting polypeptide (NTCP; also known as SLC10A1) expressed in hepatocytes, and the apical sodium-dependent bile acid transporter (ASBT; also known as SLC10A2) expressed on enterocytes in the terminal ileum (2). In recent years, ASBT has attracted much interest as a potential drug target for treatment of hypercholesterolaemia, because inhibition of ASBT reduces reabsorption of bile acids, thus increasing bile acid synthesis and consequently cholesterol consumption (3,4). However, a lack of three-dimensional structures of bile acid transporters hampers our ability to understand the molecular mechanisms of substrate selectivity and transport, and to interpret the wealth of existing functional data (2,5-8). The crystal structure of an ASBT homologue from Neisseria meningitidis ([ASBT.sub.NM]) in detergent was reported recently (9), showing the protein in an inward-open conformation bound to two [Na.sup.+] and a taurocholic acid. However, the structural changes that bring bile acid and [Na.sup.+] across the membrane are difficult to infer from a single structure. To understand the structural changes associated with the coupled transport of [Na.sup.+] and bile acids, here we solved two structures of an ASBT homologue from Yersinia frederiksenii ([ASBT.sub.Yf]) in a lipid environment, which reveal that a large rigid-body rotation of a substrate-binding domain gives the conserved 'crossover' region, where two discontinuous helices cross each other, alternating accessibility from either side of the cell membrane. This result has implications for the location and orientation of the bile acid during transport, as well as for the translocation pathway for [Na.sup.+]., Purified [ASBT.sub.Yf], when reconstituted into liposomes, mediates [Na.sup.+]-dependent transport of the conjugated bile acid taurocholic acid (TCA) with an apparent Michaelis constant ([K.sub.m]) of 46.8 6 7.4 µM (Fig. 1a, [...]

Voltage-gated calcium ([Ca.sub.V]) channels catalyse rapid, highly selective influx of [Ca.sup.2+] into cells despite a 70-fold higher extracellular concentration of [Na.sup.+] .How [Ca.sub.V] channels solve this fundamental biophysical problem remains unclear. Here we report physiological and crystallographic analyses of a calcium selectivity filter constructed in the homotetrameric bacterial [Na.sub.V] channel [Na.sub.V]Ab. Our results reveal interactions of hydrated [Ca.sup.2+] with two high-affinity [Ca.sup.2+] -binding sites followed by a third lower-affinity site that would coordinate [Ca.sup.2+] as it moves inward. At the selectivity filter entry, Site 1 is formed by four carboxyl side chains, which have a critical role in determining [Ca.sup.2+] selectivity. Four carboxyls plus four backbone carbonyls form Site 2, which is targeted by the blocking cations [Cd.sup.2+] and [Mn.sup.2+], with single occupancy. The lower-affinity Site 3 is formed by four backbone carbonyls alone, which mediate exit into the central cavity. This pore architecture suggests a conduction pathway involving transitions between two main states with one or two hydrated [Ca.sup.2+] ions bound in the selectivity filter and supports a 'knock-off' mechanism of ion permeation through a stepwisebinding process. The multi-ion selectivity filter of our [Ca.sub.V]Ab model establishes a structural framework for understanding the mechanisms of ion selectivity and conductance by vertebrate [Ca.sub.V] channels., [Ca.sup.2+] ions flow through [Ca.sub.V] channels at a rate of ~[10.sup.6] ions [s.sup.-1], yet [Na.sup.+] conductance is >500-fold lower (1). Such high-fidelity, high-throughput [Ca.sub.V] channel performance is important in regulating [...]

The contraction and relaxation of muscle cells is controlled by the successive rise and fall of cytosolic [Ca.sup.2+], initiated by the release of [Ca.sup.2+] from the sarcoplasmic reticulum and terminated by re-sequestration of [Ca.sup.2+] into the sarcoplasmic reticulum as the main mechanism of [Ca.sup.2+] removal. Re-sequestration requires active transport and is catalysed by the sarcoplasmic reticulum [Ca.sup.2+]-ATPase (SERCA), which has a key role in defining the contractile properties of skeletal and heart muscle tissue. The activity of SERCA is regulated by two small, homologous membrane proteins called phospholamban (PLB, also known as PLN) and sarcolipin (SLN) (1, 2). Detailed structural information explaining this regulatory mechanism has been lacking, and the structural features defining the pathway through which cytoplasmic [Ca.sup.2+] enters the intramembranous binding sites of SERCA have remained unknown. Here we report the crystal structure of rabbit SERCA1a (also known as ATP2A1) in complex with SLN at 3.1 Å resolution. The regulatory SLN traps the [Ca.sup.2+]-ATPase in a previously undescribed E1 state, with exposure of the [Ca.sup.2+] sites through an open cytoplasmic pathway stabilized by [Mg.sup.2+]. The structure suggests a mechanism for selective [Ca.sup.2+] loading and activation of SERCA, and provides new insight into how SLN and PLB inhibition arises from stabilization of this E1 intermediate state without bound [Ca.sup.2+]. These findings may prove useful in studying how autoinhibitory domains of other ion pumps modulate transport across biological membranes., The regulation of SERCA by SLN and PLB is a key determinant of the contractile properties of both skeletal and heart muscle tissue. In humans, SLN is primarily expressed in [...]

P-type ATPases are ATP-powered ion pumps that establish ion concentration gradients across biological membranes, and are distinct from other ATPases in that the reaction cycle includes an autophosphorylation step. The best studied is [Ca.sup.2+]-ATPase from muscle sarcoplasmic reticulum (SERCA1a), a [Ca.sup.2+] pump that relaxes muscle cells after contraction, and crystal structures have been determined for most of the reaction intermediates (1,2). An important outstanding structure is that of the E1 intermediate, which has empty high-affinity [Ca.sup.2+]-binding sites ready to accept new cytosolic [Ca.sup.2+]. In the absence of [Ca.sup.2+] and at pH 7 or higher, the ATPase is predominantly in E1, not in E2 (low affinity for [Ca.sup.2+]) (3), and if millimolar [Mg.sup.2+] is present, one [Mg.sup.2+] is expected to occupy one of the [Ca.sup.2+]-binding sites with a millimolar dissociation constant (4,5). This [Mg.sup.2+] accelerates the reaction cycle (4), not permitting phosphorylation without [Ca.sup.2+] binding. Here we describe the crystal structure of native SERCA1a (from rabbit) in this E1 x [Mg.sup.2+] state at 3.0 [Anstrom] resolution in addition to crystal structures of SERCA1a in E2 free from exogenous inhibitors, and address the structural basis of the activation signal for phosphoryl transfer. Unexpectedly, sarcolipin (6), a small regulatory membrane protein of [Ca.sup.2+]-ATPase (7), is bound, stabilizing the E1 x [Mg.sup.2+] state. Sarcolipin is a close homologue of phospholamban, which is a critical mediator of β-adrenergic signal in [Ca.sup.2+] regulation in heart (for reviews, see, for example, refs 8-10), and seems to play an important role in muscle-based thermogenesis (11). We also determined the crystal structure of recombinant SERCA1a devoid of sarcolipin, and describe the structural basis of inhibition by sarcolipin/phospholamban. Thus, the crystal structures reported here fill a gap in the structural elucidation of the reaction cycle and provide a solid basis for understanding the physiological regulation of the calcium pump., New E2 (Supplementary Fig. 1) crystals of SERCAla free from exogenous inhibitors were grown in either 40 mM MgS[O.sub.4] (E2 x S[O.sub.4.sup.2-] crystals) or Mg[Cl.sub.2] (E2 crystals) at pH 6.5 [...]

On binding to its target hormone, the oestrogen-receptor protein modulates the expression of many genes. Changes in the receptor's interaction with DNA have now been linked to clinical outcome in patients with breast cancer. See Letter p.389, In about two-thirds of breast cancers, tumour growth depends on oestrogen. This hormone binds to and activates its nuclear receptor, which then binds to specific sites on the genome and [...]