Academic Appointments


All Publications

  • Conformationally Preorganized Diastereomeric Norbornane-Based Maltosides for Membrane Protein Study: Implications of Detergent Kink for Micellar Properties. Journal of the American Chemical Society Das, M., Du, Y., Ribeiro, O., Hariharan, P., Mortensen, J. S., Patra, D., Skiniotis, G., Loland, C. J., Guan, L., Kobilka, B. K., Byrne, B., Chae, P. S. 2017; 139 (8): 3072-3081


    Detergents are essential tools for functional and structural studies of membrane proteins. However, conventional detergents are limited in their scope and utility, particularly for eukaryotic membrane proteins. Thus, there are major efforts to develop new amphipathic agents with enhanced properties. Here, a novel class of diastereomeric agents with a preorganized conformation, designated norbornane-based maltosides (NBMs), were prepared and evaluated for their ability to solubilize and stabilize membrane proteins. Representative NBMs displayed enhanced behaviors compared to n-dodecyl-β-d-maltoside (DDM) for all membrane proteins tested. Efficacy of the individual NBMs varied depending on the overall detergent shape and alkyl chain length. Specifically, NBMs with no kink in the lipophilic region conferred greater stability to the proteins than NBMs with a kink. In addition, long alkyl chain NBMs were generally better at stabilizing membrane proteins than short alkyl chain agents. Furthermore, use of one well-behaving NBM enabled us to attain a marked stabilization and clear visualization of a challenging membrane protein complex using electron microscopy. Thus, this study not only describes novel maltoside detergents with enhanced protein-stabilizing properties but also suggests that overall detergent geometry has an important role in determining membrane protein stability. Notably, this is the first systematic study on the effect of detergent kinking on micellar properties and associated membrane protein stability.

    View details for DOI 10.1021/jacs.6b11997

    View details for PubMedID 28218862

  • Highly Branched Pentasaccharide-Bearing Amphiphiles for Membrane Protein Studies JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ehsan, M., Du, Y., Scull, N. J., Tikhonova, E., Tarrasch, J., Mortensen, J. S., Loland, C. J., Skiniotis, G., Guan, L., Byrne, B., Kobilka, B. K., Chae, P. S. 2016; 138 (11): 3789-3796


    Detergents are essential tools for membrane protein manipulation. Micelles formed by detergent molecules have the ability to encapsulate the hydrophobic domains of membrane proteins. The resulting protein-detergent complexes (PDCs) are compatible with the polar environments of aqueous media, making structural and functional analysis feasible. Although a number of novel agents have been developed to overcome the limitations of conventional detergents, most have traditional head groups such as glucoside or maltoside. In this study, we introduce a class of amphiphiles, the PSA/Es with a novel highly branched pentasaccharide hydrophilic group. The PSA/Es conferred markedly increased stability to a diverse range of membrane proteins compared to conventional detergents, indicating a positive role for the new hydrophilic group in maintaining the native protein integrity. In addition, PDCs formed by PSA/Es were smaller and more suitable for electron microscopic analysis than those formed by DDM, indicating that the new agents have significant potential for the structure-function studies of membrane proteins.

    View details for DOI 10.1021/jacs.5b13233

    View details for Web of Science ID 000372854200027

  • Visualization of arrestin recruitment by a G-protein-coupled receptor NATURE Shukla, A. K., Westfield, G. H., Xiao, K., Reis, R. I., Huang, L., Tripathi-Shukla, P., Qian, J., Li, S., Blanc, A., Oleskie, A. N., Dosey, A. M., Su, M., Liang, C., Gu, L., Shan, J., Chen, X., Hanna, R., Choi, M., Yao, X. J., Klink, B. U., Kahsai, A. W., Sidhu, S. S., Koide, S., Penczek, P. A., Kossiakoff, A. A., Woods, V. L., Kobilka, B. K., Skiniotis, G., Lefkowitz, R. J. 2014; 512 (7513): 218-?


    G-protein-coupled receptors (GPCRs) are critically regulated by β-arrestins, which not only desensitize G-protein signalling but also initiate a G-protein-independent wave of signalling. A recent surge of structural data on a number of GPCRs, including the β2 adrenergic receptor (β2AR)-G-protein complex, has provided novel insights into the structural basis of receptor activation. However, complementary information has been lacking on the recruitment of β-arrestins to activated GPCRs, primarily owing to challenges in obtaining stable receptor-β-arrestin complexes for structural studies. Here we devised a strategy for forming and purifying a functional human β2AR-β-arrestin-1 complex that allowed us to visualize its architecture by single-particle negative-stain electron microscopy and to characterize the interactions between β2AR and β-arrestin 1 using hydrogen-deuterium exchange mass spectrometry (HDX-MS) and chemical crosslinking. Electron microscopy two-dimensional averages and three-dimensional reconstructions reveal bimodal binding of β-arrestin 1 to the β2AR, involving two separate sets of interactions, one with the phosphorylated carboxy terminus of the receptor and the other with its seven-transmembrane core. Areas of reduced HDX together with identification of crosslinked residues suggest engagement of the finger loop of β-arrestin 1 with the seven-transmembrane core of the receptor. In contrast, focal areas of raised HDX levels indicate regions of increased dynamics in both the N and C domains of β-arrestin 1 when coupled to the β2AR. A molecular model of the β2AR-β-arrestin signalling complex was made by docking activated β-arrestin 1 and β2AR crystal structures into the electron microscopy map densities with constraints provided by HDX-MS and crosslinking, allowing us to obtain valuable insights into the overall architecture of a receptor-arrestin complex. The dynamic and structural information presented here provides a framework for better understanding the basis of GPCR regulation by arrestins.

    View details for DOI 10.1038/nature13430

    View details for Web of Science ID 000340200700037

    View details for PubMedID 25043026

    View details for PubMedCentralID PMC4134437

  • Crystal structure of the beta(2) adrenergic receptor-Gs protein complex NATURE Rasmussen, S. G., DeVree, B. T., Zou, Y., Kruse, A. C., Chung, K. Y., Kobilka, T. S., Thian, F. S., Chae, P. S., Pardon, E., Calinski, D., Mathiesen, J. M., Shah, S. T., Lyons, J. A., Caffrey, M., Gellman, S. H., Steyaert, J., Skiniotis, G., Weis, W. I., Sunahara, R. K., Kobilka, B. K. 2011; 477 (7366): 549-U311


    G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The β(2) adrenergic receptor (β(2)AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomeric β(2)AR and nucleotide-free Gs heterotrimer. The principal interactions between the β(2)AR and Gs involve the amino- and carboxy-terminal α-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The largest conformational changes in the β(2)AR include a 14 Å outward movement at the cytoplasmic end of transmembrane segment 6 (TM6) and an α-helical extension of the cytoplasmic end of TM5. The most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain. This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR.

    View details for DOI 10.1038/nature10361

    View details for Web of Science ID 000295320900031

    View details for PubMedID 21772288

    View details for PubMedCentralID PMC3184188

  • Structural flexibility of the Gas alpha-helical domain in the beta(2)-adrenoceptor Gs complex PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Westfield, G. H., Rasmussen, S. G., Su, M., Dutta, S., DeVree, B. T., Chung, K. Y., Calinski, D., Velez-Ruiz, G., Oleskie, A. N., Pardon, E., Chae, P. S., Liu, T., Li, S., Woods, V. L., Steyaert, J., Kobilka, B. K., Sunahara, R. K., Skiniotis, G. 2011; 108 (38): 16086-16091


    The active-state complex between an agonist-bound receptor and a guanine nucleotide-free G protein represents the fundamental signaling assembly for the majority of hormone and neurotransmitter signaling. We applied single-particle electron microscopy (EM) analysis to examine the architecture of agonist-occupied β(2)-adrenoceptor (β(2)AR) in complex with the heterotrimeric G protein Gs (Gαsβγ). EM 2D averages and 3D reconstructions of the detergent-solubilized complex reveal an overall architecture that is in very good agreement with the crystal structure of the active-state ternary complex. Strikingly however, the α-helical domain of Gαs appears highly flexible in the absence of nucleotide. In contrast, the presence of the pyrophosphate mimic foscarnet (phosphonoformate), and also the presence of GDP, favor the stabilization of the α-helical domain on the Ras-like domain of Gαs. Molecular modeling of the α-helical domain in the 3D EM maps suggests that in its stabilized form it assumes a conformation reminiscent to the one observed in the crystal structure of Gαs-GTPγS. These data argue that the α-helical domain undergoes a nucleotide-dependent transition from a flexible to a conformationally stabilized state.

    View details for DOI 10.1073/pnas.1113645108

    View details for Web of Science ID 000295030000081

    View details for PubMedID 21914848

    View details for PubMedCentralID PMC3179071

  • Structural Snapshots of Full-Length Jak1, a Transmembrane gp130/IL-6/IL-6R alpha Cytokine Receptor Complex, and the Receptor-Jak1 Holocomplex STRUCTURE Lupardus, P. J., Skiniotis, G., Rice, A. J., Thomas, C., Fischer, S., Walz, T., Garcia, K. C. 2011; 19 (1): 45-55


    The shared cytokine receptor gp130 signals as a homodimer or heterodimer through activation of Janus kinases (Jaks) associated with the receptor intracellular domains. Here, we reconstitute, in parts and whole, the full-length gp130 homodimer in complex with the cytokine interleukin-6 (IL-6), its alpha receptor (IL-6Rα) and Jak1, for electron microscopy imaging. We find that the full-length gp130 homodimer complex has intimate interactions between the trans- and juxtamembrane segments of the two receptors, appearing to form a continuous connection between the extra- and intracellular regions. 2D averages and 3D reconstructions of full-length Jak1 reveal a three lobed structure comprising FERM-SH2, pseudokinase, and kinase modules possessing extensive intersegmental flexibility that likely facilitates allosteric activation. Single-particle imaging of the gp130/IL-6/IL-6Rα/Jak1 holocomplex shows Jak1 associated with the membrane proximal intracellular regions of gp130, abutting the would-be inner leaflet of the cell membrane. Jak1 association with gp130 is enhanced by the presence of a membrane environment.

    View details for DOI 10.1016/j.str.2010.10.010

    View details for Web of Science ID 000286348000008

    View details for PubMedID 21220115

  • Structural organization of a full-length gp130/LIF-R cytokine receptor transmembrane complex MOLECULAR CELL Skiniotis, G., Lupardus, P. J., Martick, M., Walz, T., Garcia, K. C. 2008; 31 (5): 737-748


    gp130 is a shared receptor for at least nine cytokines and can signal either as a homodimer or as a heterodimer with Leukemia Inhibitory Factor Receptor (LIF-R). Here, we biophysically and structurally characterize the full-length, transmembrane form of a quaternary cytokine receptor complex consisting of gp130, LIF-R, the cytokine Ciliary Neurotrophic Factor (CNTF), and its alpha receptor (CNTF-Ralpha). Thermodynamic analysis indicates that, unlike the cooperative assembly of the symmetric gp130/Interleukin-6/IL-6Ralpha hexameric complex, CNTF/CNTF-Ralpha heterodimerizes gp130 and LIF-R via noncooperative energetics to form an asymmetric 1:1:1:1 complex. Single particle electron microscopic analysis of the full-length gp130/LIF-R/CNTF-Ralpha/CNTF quaternary complex elucidates an asymmetric structural arrangement, in which the receptor extracellular and transmembrane segments join as a continuous, rigid unit, poised to sensitively transduce ligand engagement to the membrane-proximal intracellular signaling regions. These studies also enumerate the organizing principles for assembly of the "tall" class of gp130 family cytokine receptor complexes including LIF, IL-27, IL-12, and others.

    View details for DOI 10.1016/j.molcel.2008.08.011

    View details for Web of Science ID 000259113800014

    View details for PubMedID 18775332

  • Signaling conformations of the tall cytokine receptor gp130 when in complex with IL-6 and IL-6 receptor NATURE STRUCTURAL & MOLECULAR BIOLOGY Skiniotis, G., Boulanger, M. J., Garcia, K. C., Walz, T. 2005; 12 (6): 545-551


    gp130 is a shared cytokine signaling receptor and the founding member of the 'tall' class of cytokine receptors. A crystal structure of the ligand-binding domains of gp130 in complex with human interleukin-6 (IL-6) and its a-receptor (IL-6Ralpha) revealed a hexameric architecture in which the gp130 membrane-distal regions were approximately 100 A apart, in contrast to the close apposition seen between short cytokine receptor complexes. Here we used single-particle EM to visualize the entire extracellular hexameric IL-6-IL-6Ralpha-gp130 complex, containing all six gp130 domains. The structure reveals that gp130 is bent such that the membrane-proximal domains of gp130 are close together at the cell surface, enabling activation of intracellular signaling. Variation in the receptor bend angles suggests a possible conformational transition from open to closed states upon ligand binding; this transition is probably representative of the other tall cytokine receptors.

    View details for DOI 10.1038/nsmb941

    View details for Web of Science ID 000229533800016

    View details for PubMedID 15895091