Professional Education

  • Bachelor of Arts, University Of Melbourne (2013)
  • Bachelor of Science, University Of Melbourne (2013)
  • Doctor of Philosophy, University of Oxford (2018)

Stanford Advisors

All Publications

  • Structural basis of Smoothened regulation by its extracellular domains. Nature Byrne, E. F., Sircar, R., Miller, P. S., Hedger, G., Luchetti, G., Nachtergaele, S., Tully, M. D., Mydock-McGrane, L., Covey, D. F., Rambo, R. P., Sansom, M. S., Newstead, S., Rohatgi, R., Siebold, C. 2016; 535 (7613): 517-522


    Developmental signals of the Hedgehog (Hh) and Wnt families are transduced across the membrane by Frizzledclass G-protein-coupled receptors (GPCRs) composed of both a heptahelical transmembrane domain (TMD) and an extracellular cysteine-rich domain (CRD). How the large extracellular domains of GPCRs regulate signalling by the TMD is unknown. We present crystal structures of the Hh signal transducer and oncoprotein Smoothened, a GPCR that contains two distinct ligand-binding sites: one in its TMD and one in the CRD. The CRD is stacked a top the TMD, separated by an intervening wedge-like linker domain. Structure-guided mutations show that the interface between the CRD, linker domain and TMD stabilizes the inactive state of Smoothened. Unexpectedly, we find a cholesterol molecule bound to Smoothened in the CRD binding site. Mutations predicted to prevent cholesterol binding impair the ability of Smoothened to transmit native Hh signals. Binding of a clinically used antagonist, vismodegib, to the TMD induces a conformational change that is propagated to the CRD, resulting in loss of cholesterol from the CRD-linker domain-TMD interface. Our results clarify the structural mechanism by which the activity of a GPCR is controlled by ligand-regulated interactions between its extracellular and transmembrane domains.

    View details for PubMedID 27437577

  • A serine in the first transmembrane domain of the human E3 ubiquitin ligase MARCH9 is critical for down-regulation of its protein substrates JOURNAL OF BIOLOGICAL CHEMISTRY Tan, C., Byrne, E. X., Ah-Cann, C., Call, M. J., Call, M. E. 2019; 294 (7): 2470–85
  • Lentiviral transduction of mammalian cells for fast, scalable and high-level production of soluble and membrane proteins. Nature protocols Elegheert, J., Behiels, E., Bishop, B., Scott, S., Woolley, R. E., Griffiths, S. C., Byrne, E. F., Chang, V. T., Stuart, D. I., Jones, E. Y., Siebold, C., Aricescu, A. R. 2018


    Structural, biochemical and biophysical studies of eukaryotic soluble and membrane proteins require their production in milligram quantities. Although large-scale protein expression strategies based on transient or stable transfection of mammalian cells are well established, they are associated with high consumable costs, limited transfection efficiency or long and tedious selection of clonal cell lines. Lentiviral transduction is an efficient method for the delivery of transgenes to mammalian cells and unifies the ease of use and speed of transient transfection with the robust expression of stable cell lines. In this protocol, we describe the design and step-by-step application of a lentiviral plasmid suite, termed pHR-CMV-TetO2, for the constitutive or inducible large-scale production of soluble and membrane proteins in HEK293 cell lines. Optional features include bicistronic co-expression of fluorescent marker proteins for enrichment of co-transduced cells using cell sorting and of biotin ligase for in vivo biotinylation. We demonstrate the efficacy of the method for a set of soluble proteins and for the G-protein-coupled receptor (GPCR) Smoothened (SMO). We further compare this method with baculovirus transduction of mammalian cells (BacMam), using the type-A gamma-aminobutyric acid receptor (GABAAR) beta3 homopentamer as a test case. The protocols described here are optimized for simplicity, speed and affordability; lead to a stable polyclonal cell line and milligram-scale amounts of protein in 3-4 weeks; and routinely achieve an approximately three- to tenfold improvement in protein production yield per cell as compared to transient transduction or transfection.

    View details for PubMedID 30455477

  • Cilia-Associated Oxysterols Activate Smoothened. Molecular cell Raleigh, D. R., Sever, N., Choksi, P. K., Sigg, M. A., Hines, K. M., Thompson, B. M., Elnatan, D., Jaishankar, P., Bisignano, P., Garcia-Gonzalo, F. R., Krup, A. L., Eberl, M., Byrne, E. F., Siebold, C., Wong, S. Y., Renslo, A. R., Grabe, M., McDonald, J. G., Xu, L., Beachy, P. A., Reiter, J. F. 2018; 72 (2): 316


    Primary cilia are required for Smoothened to transduce vertebrate Hedgehog signals, but how Smoothened accumulates in cilia and is activated is incompletely understood. Here, we identify cilia-associated oxysterols that promote Smoothened accumulation in cilia and activate the Hedgehog pathway. Our data reveal that cilia-associated oxysterols bind to two distinct Smoothened domains to modulate Smoothened accumulation in cilia and tune the intensity of Hedgehog pathway activation. We find that the oxysterol synthase HSD11beta2 participates in the production of Smoothened-activating oxysterols and promotes Hedgehog pathway activity. Inhibiting oxysterol biosynthesis impedes oncogenic Hedgehog pathway activation and attenuates the growth of Hedgehog pathway-associated medulloblastoma, suggesting that targeted inhibition of Smoothened-activating oxysterol production may be therapeutically useful for patients with Hedgehog-associated cancers.

    View details for PubMedID 30340023

  • Multiple ligand binding sites regulate the Hedgehog signal transducer Smoothened in vertebrates. Current opinion in cell biology Byrne, E. F., Luchetti, G. n., Rohatgi, R. n., Siebold, C. n. 2017; 51: 81–88


    The Hedgehog (Hh) pathway plays a central role in the development of multicellular organisms, guiding cell differentiation, proliferation and survival. While many components of the vertebrate pathway were discovered two decades ago, the mechanism by which the Hh signal is transmitted across the plasma membrane remains mysterious. This fundamental task in signalling is carried out by Smoothened (SMO), a human oncoprotein and validated cancer drug target that is a member of the G-protein coupled receptor protein family. Recent structural and functional studies have advanced our mechanistic understanding of SMO activation, revealing its unique regulation by two separable but allosterically-linked ligand-binding sites. Unexpectedly, these studies have nominated cellular cholesterol as having an instructive role in SMO signalling.

    View details for PubMedID 29268141

  • Cholesterol activates the G-protein coupled receptor Smoothened to promote morphogenetic signaling. eLife Luchetti, G., Sircar, R., Kong, J. H., Nachtergaele, S., Sagner, A., Byrne, E. F., Covey, D. F., Siebold, C., Rohatgi, R. 2016; 5


    Cholesterol is necessary for the function of many G-protein coupled receptors (GPCRs). We find that cholesterol is not just necessary but also sufficient to activate signaling by the Hedgehog (Hh) pathway, a prominent cell-cell communication system in development. Cholesterol influences Hh signaling by directly activating Smoothened (SMO), an orphan GPCR that transmits the Hh signal across the membrane in all animals. Unlike many GPCRs, which are regulated by cholesterol through their heptahelical transmembrane domains, SMO is activated by cholesterol through its extracellular cysteine-rich domain (CRD). Residues shown to mediate cholesterol binding to the CRD in a recent structural analysis also dictate SMO activation, both in response to cholesterol and to native Hh ligands. Our results show that cholesterol can initiate signaling from the cell surface by engaging the extracellular domain of a GPCR and suggest that SMO activity may be regulated by local changes in cholesterol abundance or accessibility.

    View details for DOI 10.7554/eLife.20304

    View details for PubMedID 27705744

    View details for PubMedCentralID PMC5123864