G protein-coupled receptors (GPCRs) within the same subfamily often share high homology in their orthosteric pocket and therefore pose challenges to drug development. The amino acids that form the orthosteric binding pocket for epinephrine and norepinephrine in the β1 and β2 adrenergic receptors (β1AR and β2AR) are identical. Here, to examine the effect of conformational restriction on ligand binding kinetics, we synthesized a constrained form of epinephrine. Surprisingly, the constrained epinephrine exhibits over 100-fold selectivity for the β2AR over the β1AR. We provide evidence that the selectivity may be due to reduced ligand flexibility that enhances the association rate for the β2AR, as well as a less stable binding pocket for constrained epinephrine in the β1AR. The differences in the amino acid sequence of the extracellular vestibule of the β1AR allosterically alter the shape and stability of the binding pocket, resulting in a marked difference in affinity compared to the β2AR. These studies suggest that for receptors containing identical binding pocket residues, the binding selectivity may be influenced in an allosteric manner by surrounding residues, like those of the extracellular loops (ECLs) that form the vestibule. Exploiting these allosteric influences may facilitate the development of more subtype-selective ligands for GPCRs.

Supplementary table from Integrative RNA-omics Discovers GNAS Alternative Splicing as a Phenotypic Driver of Splicing Factor–Mutant Neoplasms

In this work, we examine methyl nuclear magnetic resonance (NMR) spectra of the methionine ε-[13CH3] labelled thermostabilized β1 adrenergic receptor from turkey in association with a variety of different effectors, including mini-Gs and nanobody 60 (Nb60), which have not been previously studied in complex with β1 adrenergic receptor (β1AR) by NMR. Complexes with pindolol and Nb60 induce highly similar inactive states of the receptor, closely resembling the resting state conformational ensemble. We show that, upon binding of mini-Gs or nanobody 80 (Nb80), large allosteric changes throughout the receptor take place. The conformation of tβ1AR stabilized by the native-like mini-Gs protein is highly similar to the conformation induced by the currently used surrogate Nb80. Interestingly, in both cases residual dynamics are present, which were not observed in the resting states. Finally, we reproduce a pharmaceutically relevant situation, where an antagonist abolishes the interaction of the receptor with the mini-G protein in a competitive manner, validating the functional integrity of our preparation. The presented system is therefore well suited for reproducing the individual steps of the activation cycle of a G protein-coupled receptor (GPCR) in vitro and serves as a basis for functional and pharmacological characterizations of more native-like systems in the future.

Cellular functions of arrestins are determined in part by the pattern of phosphorylation on the G protein-coupled receptors (GPCRs) to which arrestins bind. Despite high-resolution structural data of arrestins bound to phosphorylated receptor C-termini, the functional role of each phosphorylation site remains obscure. Here, we employ a library of synthetic phosphopeptide analogues of the GPCR rhodopsin C-terminus and determine the ability of these peptides to bind and activate arrestins using a variety of biochemical and biophysical methods. We further characterize how these peptides modulate the conformation of arrestin-1 by nuclear magnetic resonance (NMR). Our results indicate different functional classes of phosphorylation sites: 'key sites' required for arrestin binding and activation, an 'inhibitory site' that abrogates arrestin binding, and 'modulator sites' that influence the global conformation of arrestin. These functional motifs allow a better understanding of how different GPCR phosphorylation patterns might control how arrestin functions in the cell.

Protein phosphorylation barcodes, clusters of several phosphorylation sites within a short unfolded region, control many cellular processes. Existing biochemical methods used to study the roles of these barcodes suffer from low selectivity and provide only qualitative data. Chemically synthesized multiphosphopeptide libraries are selective and specific, but their synthesis is extremely difficult using the current peptide synthesis methods. Here we describe a new microwave assisted approach for synthesizing a library of multiphosphopeptides, using the C-terminus of rhodopsin as a proof of concept. Our approach utilizes multiple protocols for synthesizing libraries of multiphosphopeptides instead of the inefficient single protocol methods currently used. Using our approach we demonstrated the synthesis with up to seven phosphorylated amino acids, sometimes next to each other, an accomplishment that was impractical before. Synthesizing the Rhodopsin derived multiphosphopeptide library enabled dissecting the precise phosphorylation barcode required for the recruitment, activation and modulation of the conformation of Arrestin. Since phosphorylation barcodes modulate the activity of hundreds of GPCRs, synthesizing libraries of multiphosphopeptides is the method of choice for studying their molecular mechanisms of action. Our approach provides an invaluable tool for evaluating how protein phosphorylation barcodes regulate their activity.

In the absence of orthosteric ligands, most G protein-coupled receptors (GPCRs) exist in an equilibrium of different conformational states. This equilibrium is shifted by an agonist towards the active state or by an inverse agonist towards the inactive state. The basal activity of the receptor, and its ability to activate intracellular signaling pathways, is defined by the probability that a fraction of the receptor adopts the active state in the absence of ligand. Despite breakthroughs in native MS of membrane proteins, GPCR-transducing complexes have not been studied by this approach until very recently. Here, we investigated different conformational states of the turkey β1 adrenergic receptor (tβ1AR) in complex with two transducing partners: a G protein mimicking nanobody, Nb80, and an engineered truncated Gs protein (miniGs), in the presence of the full agonist isoprenaline by native MS. Interestingly, complex formation with both transducing partners was also observed in the absence of agonist, and allowed us to quantify basal activity of tβ1AR. We followed the stepwise disassembly of the transducing complexes by increasing the concentration of the inverse agonist S32212 in the presence of a constant concentration of isoprenaline. This allowed us to determine the relative binding affinity of S32212 in comparison to isoprenaline by native MS. Our approach provides a fast and sensitive way to detect complexes, study their stability in the presence of different ligands, and determine relative ligand affinities. Native mass spectrometry thus has the potential to become a useful tool to screen for orthosteric and allosteric GPCR drugs. Graphical Abstract.

Cdc48 is a AAA+ ATPase that plays an essential role for many cellular processes in eukaryotic cells. An archaeal homologue of this highly conserved enzyme was shown to directly interact with the 20S proteasome. Here, we analyze the occurrence and phylogeny of a Cdc48 homologue in Actinobacteria and assess its cellular function and possible interaction with the bacterial proteasome. Our data demonstrate that Cdc48-like protein of actinobacteria (Cpa) forms hexameric rings and that the oligomeric state correlates directly with the ATPase activity. Furthermore, we show that the assembled Cpa rings can physically interact with the 20S core particle. Comparison of the Mycobacterium smegmatis wild-type with a cpa knockout strain under carbon starvation uncovers significant changes in the levels of around 500 proteins. Pathway mapping of the observed pattern of changes identifies ribosomal proteins as a particular hotspot, pointing amongst others toward a role of Cpa in ribosome adaptation during starvation.

13 Cdc48 is a AAA+ ATPase that plays an essential role for many cellular processes in 14 eukaryotic cells. An archaeal homologue of this highly conserved enzyme was shown to 15 directly interact with the 20S proteasome. Here, we analyze the occurrence and phylogeny of 16 a Cdc48 homologue in Actinobacteria and assess its cellular function and possible 17 interaction with the bacterial proteasome. Our data demonstrate that Cdc48-like protein of 18 actinobacteria (Cpa) forms hexameric rings and that the oligomeric state correlates directly 19 with the ATPase activity. Furthermore, we show that the assembled Cpa rings can physically 20 interact with the 20S core particle. Comparison of the Mycobacterium smegmatis wild-type 21 with a cpa knockout strain under carbon starvation uncovers significant changes in the levels 22 of around 500 proteins. Pathway mapping of the observed pattern of changes identifies 23 ribosomal proteins as a particular hotspot, pointing amongst others toward a role of Cpa in 24 ribosome adaptation during starvation. 25

The various oligomeric states of the M2 isoform of pyruvate kinase (PKM2) were distinguished using native mass spectrometry. The effect of PKM2 concentration on its dimer-tetramer equilibrium was monitored, and a value for the dissociation constant ( Kd) of the two species was estimated to be 0.95 μM. Results of binding of fructose-1,6-bisphosphate (FBP) to PKM2 are shown and provide insight into the allosteric mechanism and changes in the oligomerization status of PKM2. The average Kd for binding of FBP to the PKM2 tetramer was estimated to be 7.5 μM. It is concluded that four molecules of FBP bind to the active PKM2 tetramer whereas binding of FBP to the PKM2 dimer was not observed. It is suggested that either FBP potentiates rapid tetramer formation after binding to apo PKM2 dimers or FBP binds to PKM2 apo tetramers, thus driving the dimer-tetramer equilibrium in the direction of fully FBP-bound tetramer. The binding occurs in a highly positively cooperative manner with a Hill coefficient ( n) of 3.

Phosphorylation of proteins at multiple sites creates different phosphorylation patterns that are essential for their biological activity. For example, such patterns contribute to the redirection of signalling to alternative pathways. Multi-phosphorylated peptides are excellent tools to systematically study the impact of unique phosphorylation patterns on signalling, but their synthesis is extremely difficult. Here we present an efficient and general method for the synthesis of multi-phosphorylated peptides, using a combination of different tailor-made coupling conditions. The method was demonstrated for the synthesis of a library of Rhodopsin C terminal peptides with distinct phosphorylation patterns containing up to seven phosphorylated Ser (pSer) and Thr (pThr) residues in close proximity to one another. Our method can be used to synthesize peptides incorporating multiple phosphorylated amino acids at high efficiency. It does not require any special expertise and can be performed in any standard peptide laboratory. This approach opens the way for quantitative mechanistic studies of phosphorylation patterns and their biological roles.

Extensive mutant cycle analysis provides a map of the residues that contribute to stability and activation-associated conformational dynamics of the Gαi1 protein in nucleotide-bound states and in complex with the G protein–coupled receptor rhodopsin. We present comprehensive maps at single–amino acid resolution of the residues stabilizing the human Gαi1 subunit in nucleotide- and receptor-bound states. We generated these maps by measuring the effects of alanine mutations on the stability of Gαi1 and the rhodopsin–Gαi1 complex. We identified stabilization clusters in the GTPase and helical domains responsible for structural integrity and the conformational changes associated with activation. In activation cluster I, helices α1 and α5 pack against strands β1–β3 to stabilize the nucleotide-bound states. In the receptor-bound state, these interactions are replaced by interactions between α5 and strands β4–β6. Key residues in this cluster are Y320, which is crucial for the stabilization of the receptor-bound state, and F336, which stabilizes nucleotide-bound states. Destabilization of helix α1, caused by rearrangement of this activation cluster, leads to the weakening of the interdomain interface and release of GDP.

G-Protein gekoppelte Rezeptoren (GPCRs) gehoren zu den Membranproteinen und sind zu einem erheblichen Anteil an den Signalubertragungen, vom extrazellularen in den intrazellularen Raum, beteiligt. Sie sind an vielen wichtigen regulatorischen Prozessen in der Zelle involviert. Des Weiteren werden ihre Fehlfunktionen mit einer grosen Anzahl an Krankheiten in den Zusammenhang gebracht, wie zum Beispiel: Entstehung vom Krebs, kardiale Dysfunktion, Storungen des zentralen Nervensystems, Ubergewicht, Entzundungen und Schmerz. Etwa ein Drittel aller derzeit auf dem Markt verfugbaren Medikamente wirken auf diese Rezeptoren. Um ein besseres Verstandnis uber ihre Funktion auf molekularer Ebene zu erhalten, ist es sehr wichtig, ihre Struktur und Dynamik zu kennen. Derzeit stellt NMR die beste und am weitesten entwickelte Technik dar um die Dynamik von Proteinen zu erforschen. Fur NMR Untersuchungen ist es jedoch notwendig isotopenmarkierte Proteine zu expremieren, was jedoch oft ein Problem darstellt. E. coli ist das am besten etablierte Expressionssystem und ermoglicht eine Vielzahl an unterschiedlichen Isotopenmarkierungen. In dieser Arbeit gelang es zwei humane GPCRs erfolgreich in Milli-grammmengen zu expremieren. Die verwendeten GPCRs sind zum Einen der Wildtyp des menschlichen Vasopressin V2 Rezeptors (V2R) und zum Anderen eine stabilisierte Version des menschlichen β1-Adrenergic Rezeptors (beta1AR-FB1). Des Weiteren war es moglich ein Protokoll fur die Aufreinigung rekombinant hergestellter Proteine zu etablieren, welches ausgezeichnete Ausbeuten und eine hohe Reinheit lieferte. In weiterer Folge wurde ein Ruckfaltungsprotokoll entwickelt, das einen small-scale Screen verschiedenster Ruckfaltungsbedingungen erlaubt. Die verschiedenen Ruckfaltungsprodukte wurden mit folgenden Methoden charakterisiert: Temperaturstabilitatsassay, Radio-Ligand Binding Test, Massenspektrometrie, Gel-Permeations-Chromatographie und Analytische Ultrazentrifuge. Die Ergebnisse deuten darauf hin, dass die Ruckfaltungsstrategie ein vielversprechender Ansatz fur das weitere Forschungsprojekt darstellt. Mit ein paar wenigen weiteren Optimierungen lassen sich hochstwahrscheinlich vielversprechenden Proben fur zukunftige NMR-Studien produzieren.

Scanning mutagenesis is a powerful protein engineering technique used to study protein structure-function relationship, map binding sites and design more stable proteins or proteins with altered properties. One of the time-consuming tasks encountered in application of this technique is the design of primers for site-directed mutagenesis. Here we present an open-source multi-platform software AAscan developed to design primers for this task according to a set of empirical rules such as melting temperature, overall length, length of overlap regions, and presence of GC clamps at the 3' end, for any desired substitution. We also describe additional software tools which are used to analyse a large number of sequencing results for the presence of desired mutations, as well as related software to design primers for ligation independent cloning. We have used AAscan software to design primers to make over 700 mutants, with a success rate of over 80%. We hope that the open-source nature of our software and ready availability of freeware tools used for its development will facilitate its adaptation and further development. The software is distributed under GPLv3 licence and is available at http://www.psi.ch/lbr/aascan.