2011. Structural basis for cell surface patterning through NetrinG-NGL interactions. EMBO J, 30 (21), pp. 4479-4488. Read abstract | Read more
Brain wiring depends on cells making highly localized and selective connections through surface protein-protein interactions, including those between NetrinGs and NetrinG ligands (NGLs). The NetrinGs are members of the structurally uncharacterized netrin family. We present a comprehensive crystallographic analysis comprising NetrinG1-NGL1 and NetrinG2-NGL2 complexes, unliganded NetrinG2 and NGL3. Cognate NetrinG-NGL interactions depend on three specificity-conferring NetrinG loops, clasped tightly by matching NGL surfaces. We engineered these NGL surfaces to implant custom-made affinities for NetrinG1 and NetrinG2. In a cellular patterning assay, we demonstrate that NetrinG-binding selectivity can direct the sorting of a mixed population of NGLs into discrete cell surface subdomains. These results provide a molecular model for selectivity-based patterning in a neuronal recognition system, dysregulation of which is associated with severe neuropsychological disorders. Hide abstract
2011. Automation of large scale transient protein expression in mammalian cells. J Struct Biol, 175 (2), pp. 209-215. Read abstract | Read more
Traditional mammalian expression systems rely on the time-consuming generation of stable cell lines; this is difficult to accommodate within a modern structural biology pipeline. Transient transfections are a fast, cost-effective solution, but require skilled cell culture scientists, making man-power a limiting factor in a setting where numerous samples are processed in parallel. Here we report a strategy employing a customised CompacT SelecT cell culture robot allowing the large-scale expression of multiple protein constructs in a transient format. Successful protocols have been designed for automated transient transfection of human embryonic kidney (HEK) 293T and 293S GnTI⁻ cells in various flask formats. Protein yields obtained by this method were similar to those produced manually, with the added benefit of reproducibility, regardless of user. Automation of cell maintenance and transient transfection allows the expression of high quality recombinant protein in a completely sterile environment with limited support from a cell culture scientist. The reduction in human input has the added benefit of enabling continuous cell maintenance and protein production, features of particular importance to structural biology laboratories, which typically use large quantities of pure recombinant proteins, and often require rapid characterisation of a series of modified constructs. This automated method for large scale transient transfection is now offered as a Europe-wide service via the P-cube initiative. Hide abstract
2011. Proteoglycan-specific molecular switch for RPTPσ clustering and neuronal extension. Science, 332 (6028), pp. 484-488. Read abstract | Read more
Heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) regulate numerous cell surface signaling events, with typically opposite effects on cell function. CSPGs inhibit nerve regeneration through receptor protein tyrosine phosphatase sigma (RPTPσ). Here we report that RPTPσ acts bimodally in sensory neuron extension, mediating CSPG inhibition and HSPG growth promotion. Crystallographic analyses of a shared HSPG-CSPG binding site reveal a conformational plasticity that can accommodate diverse glycosaminoglycans with comparable affinities. Heparan sulfate and analogs induced RPTPσ ectodomain oligomerization in solution, which was inhibited by chondroitin sulfate. RPTPσ and HSPGs colocalize in puncta on sensory neurons in culture, whereas CSPGs occupy the extracellular matrix. These results lead to a model where proteoglycans can exert opposing effects on neuronal extension by competing to control the oligomerization of a common receptor. Hide abstract
2010. An extracellular steric seeding mechanism for Eph-ephrin signaling platform assembly. Nat Struct Mol Biol, 17 (4), pp. 398-402. Read abstract | Read more
Erythropoetin-producing hepatoma (Eph) receptors are cell-surface protein tyrosine kinases mediating cell-cell communication. Upon activation, they form signaling clusters. We report crystal structures of the full ectodomain of human EphA2 (eEphA2) both alone and in complex with the receptor-binding domain of the ligand ephrinA5 (ephrinA5 RBD). Unliganded eEphA2 forms linear arrays of staggered parallel receptors involving two patches of residues conserved across A-class Ephs. eEphA2-ephrinA5 RBD forms a more elaborate assembly, whose interfaces include the same conserved regions on eEphA2, but rearranged to accommodate ephrinA5 RBD. Cell-surface expression of mutant EphA2s showed that these interfaces are critical for localization at cell-cell contacts and activation-dependent degradation. Our results suggest a 'nucleation' mechanism whereby a limited number of ligand-receptor interactions 'seed' an arrangement of receptors which can propagate into extended signaling arrays. Hide abstract
2009. Crystal structure of the GluR2 amino-terminal domain provides insights into the architecture and assembly of ionotropic glutamate receptors. J Mol Biol, 392 (5), pp. 1125-1132. Read abstract | Read more
Ionotropic glutamate receptors are functionally diverse but have a common architecture, including the 400-residue amino-terminal domain (ATD). We report a 1.8-A resolution crystal structure of human GluR2-ATD. This dimeric structure provides a mechanism for how the ATDs can drive receptor assembly and subtype-restricted composition. Lattice contacts in a 4.1-A resolution crystal form reveal a tetrameric (dimer-dimer) arrangement consistent with previous cellular and cryo-electron microscopic data for full-length AMPA receptors. Hide abstract
2009. Structural insights into hedgehog ligand sequestration by the human hedgehog-interacting protein HHIP. Nat Struct Mol Biol, 16 (7), pp. 698-703. Read abstract | Read more
Hedgehog (Hh) morphogens have fundamental roles in development, whereas dysregulation of Hh signaling leads to disease. Multiple cell-surface receptors are responsible for transducing and/or regulating Hh signals. Among these, the Hedgehog-interacting protein (Hhip) is a highly conserved, vertebrate-specific inhibitor of Hh signaling. We have solved a series of crystal structures for the human HHIP ectodomain and Desert hedgehog (DHH) in isolation, as well as HHIP in complex with DHH (HHIP-DHH) and Sonic hedgehog (Shh) (HHIP-Shh), with and without Ca2+. The interaction determinants, confirmed by biophysical studies and mutagenesis, reveal previously uncharacterized and distinct functions for the Hh Zn2+ and Ca2+ binding sites--functions that may be common to all vertebrate Hh proteins. Zn2+ makes a key contribution to the Hh-HHIP interface, whereas Ca2+ is likely to prevent electrostatic repulsion between the two proteins, suggesting an important modulatory role. This interplay of several metal binding sites suggests a tuneable mechanism for regulation of Hh signaling. Hide abstract
2008. Structural basis of Nipah and Hendra virus attachment to their cell-surface receptor ephrin-B2. Nat Struct Mol Biol, 15 (6), pp. 567-572. Read abstract | Read more
Nipah and Hendra viruses are emergent paramyxoviruses, causing disease characterized by rapid onset and high mortality rates, resulting in their classification as Biosafety Level 4 pathogens. Their attachment glycoproteins are essential for the recognition of the cell-surface receptors ephrin-B2 (EFNB2) and ephrin-B3 (EFNB3). Here we report crystal structures of both Nipah and Hendra attachment glycoproteins in complex with human EFNB2. In contrast to previously solved paramyxovirus attachment complexes, which are mediated by sialic acid interactions, the Nipah and Hendra complexes are maintained by an extensive protein-protein interface, including a crucial phenylalanine side chain on EFNB2 that fits snugly into a hydrophobic pocket on the viral protein. By analogy with the development of antivirals against sialic acid binding viruses, these results provide a structural template to target antiviral inhibition of protein-protein interactions. Hide abstract
2007. Immunoglobulin superfamily cell adhesion molecules: zippers and signals. Curr Opin Cell Biol, 19 (5), pp. 543-550. Read abstract | Read more
The latest structural studies of immunoglobulin superfamily cell adhesion molecules are driving a shift in perspective; increasingly the view is not focused solely on the individual molecule but rather is on the molecular assembly. Two common themes are emerging, revealing mechanisms for ectodomain-dependent regulation of cell surface receptors' signalling abilities. The first is the propensity of many such molecules to arrange in zipper-type or array-type assemblies driven by a network of highly specific cis and trans interactions. The second is the use of the extracellular dimensions of a molecule or adhesion complex as properties which, in combination with characteristic intercellular spacings, can determine the co-localisation or exclusion of particular protein populations at cell interfaces and junctions. Hide abstract
2007. Structure of a tyrosine phosphatase adhesive interaction reveals a spacer-clamp mechanism. Science, 317 (5842), pp. 1217-1220. Read abstract | Read more
Cell-cell contacts are fundamental to multicellular organisms and are subject to exquisite levels of control. Human RPTPmu is a type IIB receptor protein tyrosine phosphatase that both forms an adhesive contact itself and is involved in regulating adhesion by dephosphorylating components of cadherin-catenin complexes. Here we describe a 3.1 angstrom crystal structure of the RPTPmu ectodomain that forms a homophilic trans (antiparallel) dimer with an extended and rigid architecture, matching the dimensions of adherens junctions. Cell surface expression of deletion constructs induces intercellular spacings that correlate with the ectodomain length. These data suggest that the RPTPmu ectodomain acts as a distance gauge and plays a key regulatory function, locking the phosphatase to its appropriate functional location. Hide abstract
2007. Glycoprotein structural genomics: solving the glycosylation problem. Structure, 15 (3), pp. 267-273. Read abstract | Read more
Glycoproteins present special problems for structural genomic analysis because they often require glycosylation in order to fold correctly, whereas their chemical and conformational heterogeneity generally inhibits crystallization. We show that the "glycosylation problem" can be solved by expressing glycoproteins transiently in mammalian cells in the presence of the N-glycosylation processing inhibitors, kifunensine or swainsonine. This allows the correct folding of the glycoproteins, but leaves them sensitive to enzymes, such as endoglycosidase H, that reduce the N-glycans to single residues, enhancing crystallization. Since the scalability of transient mammalian expression is now comparable to that of bacterial systems, this approach should relieve one of the major bottlenecks in structural genomic analysis. Hide abstract
2006. A time- and cost-efficient system for high-level protein production in mammalian cells. Acta Crystallogr D Biol Crystallogr, 62 (Pt 10), pp. 1243-1250. Read abstract | Read more
Most proteins for structural biology studies are produced by high-level expression in Escherichia coli. However, prokaryotic based expression systems fail to generate correctly folded functional forms of many proteins and hence a variety of eukaryotic based expression systems have been developed. Of these, yeast and baculovirus-infected insect cells currently represent the expression systems of choice for structural biologists. Here, protocols for a simple, fast and affordable method for transient protein expression in mammalian cells are reported. The results demonstrate that it combines several features necessary for the production of suitable samples for structural biology, in particular protein crystallography, namely high protein yield, straightforward purification, selenomethionine incorporation and control of N-linked glycosylation. The system is suitable for use in conventional laboratories or can be implemented in a medium- or high-throughput pipeline. Hide abstract
2006. Molecular analysis of receptor protein tyrosine phosphatase mu-mediated cell adhesion. EMBO J, 25 (4), pp. 701-712. Read abstract | Read more
Type IIB receptor protein tyrosine phosphatases (RPTPs) are bi-functional cell surface molecules. Their ectodomains mediate stable, homophilic, cell-adhesive interactions, whereas the intracellular catalytic regions can modulate the phosphorylation state of cadherin/catenin complexes. We describe a systematic investigation of the cell-adhesive properties of the extracellular region of RPTPmu, a prototypical type IIB RPTP. The crystal structure of a construct comprising its N-terminal MAM (meprin/A5/mu) and Ig domains was determined at 2.7 A resolution; this assigns the MAM fold to the jelly-roll family and reveals extensive interactions between the two domains, which form a rigid structural unit. Structure-based site-directed mutagenesis, serial domain deletions and cell-adhesion assays allowed us to identify the four N-terminal domains (MAM, Ig, fibronectin type III (FNIII)-1 and FNIII-2) as a minimal functional unit. Biophysical characterization revealed at least two independent types of homophilic interaction which, taken together, suggest that there is the potential for formation of a complex and possibly ordered array of receptor molecules at cell contact sites. Hide abstract
2002. Heparan sulfate proteoglycans are ligands for receptor protein tyrosine phosphatase sigma. Mol Cell Biol, 22 (6), pp. 1881-1892. Read abstract | Read more
RPTPsigma is a cell adhesion molecule-like receptor protein tyrosine phosphatase involved in nervous system development. Its avian orthologue, known as cPTPsigma or CRYPalpha, promotes intraretinal axon growth and controls the morphology of growth cones. The molecular mechanisms underlying the functions of cPTPsigma are still to be determined, since neither its physiological ligand(s) nor its substrates have been described. Nevertheless, a major class of ligand(s) is present in the retinal basal lamina and glial endfeet, the potent native growth substrate for retinal axons. We demonstrate here that cPTPsigma is a heparin-binding protein and that its basal lamina ligands include the heparan sulfate proteoglycans (HSPGs) agrin and collagen XVIII. These molecules interact with high affinity with cPTPsigma in vitro, and this binding is totally dependent upon their heparan sulfate chains. Using molecular modelling and site-directed mutagenesis, a binding site for heparin and heparan sulfate was identified in the first immunoglobulin-like domain of cPTPsigma. HSPGs are therefore a novel class of heterotypic ligand for cPTPsigma, suggesting that cPTPsigma signaling in axons and growth cones is directly responsive to matrix-associated cues. Hide abstract
Entry on NDM Website
Search Publications on PubMed
Search Structures in PDB