Spectroscopic study of the interaction between lycopene and bovine serum albumin.

The interaction of lycopene with bovine serum albumin (BSA) in aqueous solution was studied by fluorescence quenching, three-dimensional fluorescence and circular dichroism spectroscopy. The data showed that the fluorescence of BSA was quenched by lycopene at different temperatures through a dynamic mechanism. The evaluation of three-dimensional fluorescence spectra revealed a conformational modification of BSA induced by coupling with lycopene and an increase in protein diameter as a consequence of the ligand-protein interaction. Moreover, the information obtained from evaluation of the effect of lycopene on BSA conformation by circular dichroism strongly supported the existence of a slight unfolding of BSA induced by coupling to lycopene.

Integration of phage and yeast display platforms: A reliable and cost effective approach for binning of peptides as displayed on-phage.

Hundreds of target specific peptides are routinely discovered by peptide display platforms. However, due to the high cost of peptide synthesis only a limited number of peptides are chemically made for further analysis. Here we describe an accurate and cost effective method to bin peptides on-phage based on binding region(s), without any requirement for peptide or protein synthesis. This approach, which integrates phage and yeast display platforms, requires display of target and its alanine variants on yeast. Flow cytometry was used to detect binding of peptides on-phage to the target on yeast. Once hits were identified, they were synthesized to confirm their binding region(s) by HDX (Hydrogen deuterium exchange) and crystallography. Moreover, we have successfully shown that this approach can be implemented as part of a panning process to deplete non-functional peptides. This technique can be applied to any target that can be successfully displayed on yeast; it narrows down the number of peptides requiring synthesis; and its utilization during selection results in enrichment of peptide population against defined binding regions on the target.

Second-Harmonic Generation (SHG) for Conformational Measurements: Assay Development, Optimization, and Screening.

Second-harmonic generation (SHG) has recently emerged as a biophysical tool for conformational sensing of a target biomolecule upon binding to ligands such as small molecules, fragments, proteins, peptides, and oligonucleotides. To date, SHG has been used to measure conformational changes of targets such as soluble proteins, protein complexes, intrinsically disordered proteins, peripheral and integral membrane proteins, peptides, and oligonucleotides upon binding of ligands over a wide range of affinities. In this chapter, we will provide a technology overview, detailed protocols for optimizing assays and screening, practical considerations, and an example case study to guide the reader in developing robust and informative measurements using the Biodesy Delta SHG platform.

Deciphering Binding Interactions of IL-23R with HDX-MS: Mapping Protein and Macrocyclic Dodecapeptide Ligands.

Molecular characterization of the binding epitope of IL-23R and its cognate cytokine IL-23 is paramount to understand the role in autoimmune diseases and to support the discovery of new inhibitors of this protein-protein interaction. Our results revealed that HDX-MS was able to identify the binding epitope of IL-23R:IL-23, which opened the way to evaluate a peptide macrocycle described in the literature as disrupter of this autoimmune target. Thus, the characterization of the interactions of this chemotype by HDX-MS in combination with computational approaches was achieved. To our knowledge, this is the first reported structural evidence regarding the site where a small compound binds to IL-23R.

Functional interactions between the alpha1b-adrenoceptor and Galpha11 are compromised by de-palmitoylation of the G protein but not of the receptor.

Both the alpha1b-adrenoceptor and Galpha11 are targets for post-translational thio-acylation that is regulated by agonist occupancy of the receptor [P.A. Stevens, J. Pediani, J.J. Carrillo, G. Milligan, J. Biol. Chem. 276 (2001) 35883]. In co-expression studies mutation of the sites of thio-acylation in the G protein or treatment of cell membranes with hydroxylamine greatly reduced agonist stimulation of guanosine 5'-[gamma-[35S]thio]triphosphate ([35S]GTPgammaS) binding. In alpha1b-adrenoceptor-Galpha11 fusion proteins mutation of thio-acylation sites in receptor or G protein did not alter the binding affinity of the antagonist [3H]prazosin or the agonist phenylephrine. Although the potency of phenylephrine to stimulate binding of [35S]GTPgammaS to alpha1b-adrenoceptor-Galpha11 fusion proteins was unaffected by the thio-acylation potential of either element, the maximal effect was reduced by some 50% when the G protein but not the receptor was mutated to prevent thio-acylation. This reflected lack of thio-acylation of the G protein rather than mutation of Cys9 and Cys10 to Ser because treatment with hydroxylamine mimicked this in fusions containing the wild type G protein but was without effect in those mutated to prevent thio-acylation. Mutation to reduce binding of beta/gamma to Galpha11 markedly reduced phenylephrine stimulation of [35S]GTPgammaS binding. Combination of mutations to prevent thio-acylation and beta/gamma binding did not, however, have an additive effect on [35S]GTPgammaS binding. These results indicate that the thio-acylation status of the alpha1b-adrenoceptor does not regulate G protein activation whereas thio-acylation of Galpha11 plays a key role in activation by the receptor beyond providing membrane association and proximity.

Topographic molecular profile of pheochromocytomas: role of somatic down-regulation of mismatch repair.

CONTEXT AND OBJECTIVE: Despite extensive molecular investigation of adrenal pheochromocytomas, no information is available on their molecular and mismatch repair (MMR) profiles by topographic compartments. DESIGN AND SETTING: Microdissected samples from the peripheral and internal zones of 143 pheochromocytomas from a referral hospital (95 sporadic and 48 associated with multiple endocrine neoplasia type 2A) were selected for loss of heterozygosity and single nucleotide polymorphism analyses. Five polymorphic DNA regions from TP53, RB1, WT1, and NF1 were systematically studied by PCR-denaturing gradient gel electrophoresis. PATIENTS, OUTCOME MEASURES, AND INTERVENTIONS: Pheochromocytomas were classified as malignant (16 sporadic tumors with distant metastases), locally invasive (30 sporadic tumors showing retroperitoneal infiltration only), and benign (all remaining tumors). Statistical differences were evaluated using Fisher's exact test. MMR was assessed by MLH1/MSH2 sequencing and immunostaining in pheochromocytomas with two or more abnormal microsatellites. No interventions were performed in this study. RESULTS: Loss of heterozygosity/single nucleotide polymorphism involved TP53 in 40 of 134 informative cases (29.9%), RB1 in 22 of 106 informative cases (20.8%), WT1 in 32 of 120 informative cases (26.7%), and NF1 in 32 of 80 informative cases (40.0%). More genetic abnormalities involving the peripheral compartment were revealed in 34 pheochromocytomas (23.8%): 12 of 16 malignant, 10 of 30 locally invasive, and 12 of 97 benign. Multiple and coexistent genetic abnormalities characterized malignant pheochromocytomas (P < 0.001), whereas locally invasive pheochromocytomas showed a significantly higher incidence of NF1 alterations (P < 0.001). No mutations were identified in MLH1/MSH2, but MMR proteins significantly decreased in peripheral compartments. CONCLUSIONS: Multiple microsatellite alterations and topographic intratumor heterogeneity characterize malignant pheochromocytomas, suggesting a multistep tumorigenesis through somatic topographic down-regulation of MMR proteins. Locally invasive pheochromocytomas reveal topographic heterogeneity and single-locus microsatellite alterations, especially involving NF1.

GPR142 Agonists Stimulate Glucose-Dependent Insulin Secretion via Gq-Dependent Signaling.

GPR142 is an islet-enriched G protein-coupled receptor that has been investigated as a novel therapeutic target for the treatment of type 2 diabetes by virtue of its insulin secretagogue activity. However, the signaling pathways downstream of GPR142 and whether its stimulation of insulin release is glucose-dependent remain poorly characterized. In this study, we show that both native and synthetic GPR142 agonists can activate Gq as well as Gi signaling when GPR142 is recombinantly expressed in HEK293 cells. However, in primary pancreatic islets, a native cellular system, the insulin secretagogue activity of GPR142 agonists only requires Gq activation. In addition, our results show that stimulation of insulin secretion by GPR142 in pancreatic islets is strictly glucose-dependent.

GPCR dimerisation.

The concept that GPCRs exist and potentially function as dimers and/or higher oligomers has progressed recently from hypothesis to being widely accepted. A range of techniques has contributed to this understanding, including co-immunoprecipitation and various forms of fluorescence and bioluminescence resonance energy transfer. Although co-immunoprecipitation studies indicate the capacity of a wide range of GPCRs to form hetero-dimers as well as homo-dimers, this approach is not well suited to examine selectivity of interactions. Both bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) have been applied to the detection of GPCR dimerisation in intact cells and BRET and FRET have been used to attempt to quantitate the fraction of GPCRs present as dimers. Following heterologous expression, a considerable fraction of many GPCRs is not fully processed and is trafficked to the proteasome or lysosome for destruction. A distinct limitation of both BRET and conventional FRET approaches is that both the energy donor and energy acceptor tags are inside the cell. Time-resolved FRET employing N-terminally epitope-tagged GPCRs has been used to allow detection only of dimers trafficked successfully to the cell surface. Reports indicating the appearance of distinct pharmacology and function following co-expression of two GPCRs are fascinating. Much remains to be examined, however, on the specificity and mechanisms of these interactions and to develop techniques to monitor the function only of hetero-dimers when the corresponding homo-dimers must also be present.

Coexistent intraurothelial carcinoma and muscle-invasive urothelial carcinoma of the bladder: clonality and somatic down-regulation of DNA mismatch repair.

Muscle-invasive urothelial carcinomas are heterogeneous neoplasms for which the clonal relationship with low-grade urothelial dysplasia and carcinomas in situ remains unknown, and both monoclonal and field change models have been proposed. Low-grade dysplasia (18) and carcinoma in situ (12) associated with muscle-invasive urothelial carcinoma were microdissected and topographically analyzed (intraepithelial and invasive superficial and deep to muscularis mucosa) for methylation pattern of androgen receptor alleles, TP53, RB1, WT1, and NF1 microsatellite analysis to assess clonal identity; MLH1 and MSH2 sequencing/immunostaining. Appropriate controls were run. Carcinoma in situ (100%) and invasive urothelial carcinoma (100%) revealed monoclonal patterns, whereas low-grade dysplasia was preferentially polyclonal (80%). Carcinoma in situ showed aneuploid DNA content and more abnormal microsatellites than the corresponding invasive compartments, opposite to low-grade dysplasia. Absent MLH1 protein expression with no gene mutations were identified in carcinoma in situ and nodular-trabecular urothelial carcinoma with high microsatellite abnormalities. Somatic mismatch repair protein down-regulation and the accumulation of tumor suppressor gene microsatellite abnormalities contribute to a molecular evolution for monoclonal carcinoma in situ divergent from coexistent muscle-invasive urothelial carcinoma. Low-grade dysplasia is however unlikely connected with this molecular progression.

Discovery of potent CRTh2 (DP2) receptor antagonists.

Starting with the weak agonist indomethacin, a series of potent, selective CRTh2 (DP(2)) antagonists have been discovered as potential treatments for asthma, allergic rhinitis and other inflammatory diseases.

Measurement of agonist-dependent and -independent signal initiation of alpha(1b)-adrenoceptor mutants by direct analysis of guanine nucleotide exchange on the G protein galpha(11).

Immunoprecipitation of a fusion protein between the alpha(1b)-adrenoceptor and Galpha(11) following a [(35)S]GTPgammaS [guanosine-5'-O-(3-thio)triphosphate] binding assay resulted in incorporation of low levels of nucleotide. The agonist phenylephrine increased incorporation some 30-fold. Agonist-induced binding represented 1.0 mol of [(35)S]GTPgammaS/mol of fusion protein. This was to the G protein linked to the receptor rather than endogenous Galpha(q)/Galpha(11) as a fusion protein containing the alpha(1b)-adrenoceptor and a form of Galpha(11) (G(208)A) unable to exchange guanine nucleotides effectively, bound [(35)S]GTPgammaS very poorly. Fusion proteins between A(293)E, D(142)A, and 3CAM mutants of the alpha(1b)-adrenoceptor and Galpha(11) bound substantially greater levels of [(35)S]GTPgammaS in the absence of agonist than the fusion incorporating the wild-type receptor. Constitutive binding of the nucleotide induced by these mutants was only 20% of the level achieved by phenylephrine. These mutant receptors thus do not provide an accurate mimic of the agonist-occupied state. Phentolamine reduced the binding of [(35)S]GTPgammaS and acted as a partial inverse agonist for each of the constitutively active mutants. [(35)S]GTPgammaS binding to Galpha(11) was elevated by phenylephrine in both wild-type and constitutively active mutant forms of the fusion proteins, but agonist potency and binding affinity were 50 times higher for the fusions containing the mutated receptors. These studies provide the first direct demonstration of the capacity of constitutively active mutants of a receptor to stimulate guanine nucleotide exchange on the alpha subunit of a G(q) family G protein and defines a strategy potentially suitable for any receptor that couples to these G proteins.

Multiple interactions between transmembrane helices generate the oligomeric alpha1b-adrenoceptor.

Combinations of coimmunoprecipitation, single-cell fluorescence resonance energy transfer, and cell-surface time-resolved fluorescence resonance energy transfer demonstrated protein-protein interactions and quaternary structure for the alpha(1b)-adrenoceptor. Self-association of transmembrane domain 1 and its interaction with the full-length receptor indicated a symmetrical interface provided by this domain. Lack of effect of mutation of the glycophorin-A dimerization-like region within this helix demonstrated that this did not provide the molecular mechanism. Multiple interactions were observed between the alpha(1b)-adrenoceptor and fragments derived from its sequence. Fragments comprising transmembrane domains 3 and 4 and transmembrane domains 5 and 6, but not transmembrane domain 7, were also able to interact with the full-length receptor. Transmembrane domain 7 failed to interact significantly with any element of the receptor and was not transported to the cell surface after coexpression with the full-length receptor. Symmetrical interactions were also noted between fragments incorporating transmembrane domain 4, but this segment of the receptor failed to interact with transmembrane domains 1 and 2 or transmembrane domains 5 and 6. Time-resolved fluorescence resonance energy transfer studies were also consistent with contributions of transmembrane domains 1 and/or 2 and transmembrane domains 3 and/or 4 to protein-protein interactions within the quaternary structure of the alpha(1b)-adrenoceptor, and with a contribution of transmembrane domains 5 and/or 6. These data are consistent with a complex oligomeric quaternary structure of the alpha(1b)-adrenoceptor in which major, symmetrical interactions may define intradimeric contacts with other contributions, providing interdimer contacts to generate oligomeric complexes akin to those observed for murine rhodopsin. A model derived from this was developed.

Dimers of class A G protein-coupled receptors function via agonist-mediated trans-activation of associated G proteins.

The histamine H1 receptor and the alpha1b-adrenoreceptor are G protein-coupled receptors that elevate intracellular [Ca2+] via activation of Gq/G11. Assessed by co-immunoprecipitation and time-resolved fluorescence resonance energy transfer they both exist as homo-dimers. The addition of the G protein G11alpha to the C terminus of these receptors did not prevent dimerization. Agonists produced a large stimulation of guanosine 5'-3-O-([35S]thio)triphosphate ([35S]GTPgammaS) binding to receptor-G protein fusions containing wild type forms of both polypeptides. For both receptors this was abolished by incorporation of G208AG11alpha into the fusions. Mutation of a highly conserved leucine in intracellular loop 2 of each receptor also eliminated agonist function but not binding. Co-expression of the two non-functional but complementary fusion constructs reconstituted agonist-mediated binding of [35S]GTPgammaS in membranes of HEK293 cells and elevation of [Ca2+]i in mouse embryo fibroblasts lacking both Gq and G11. Co-expression of the histamine H1 receptor- and the alpha1b-adrenoreceptor-G11alpha fusions allowed detection of functional hetero-dimeric complexes, whereas co-expression of histamine H1 receptor-G11alpha with increasing amounts of L151Dalpha1b-adrenoreceptor resulted in decreasing levels of histamine-stimulated [35S]GTPgammaS binding. Co-expression of the alpha1b-adrenoreceptor with a fusion protein incorporating the N-terminal domain and transmembrane helix 1 of the alpha1b-adrenoreceptor and G11alpha did not result in agonist activation of the G protein but did indicate a role for transmembrane helix 1 in dimerization. These data demonstrate that dimers of these class A receptors function via trans-activation of associated G proteins.

Effective information transfer from the alpha 1b-adrenoceptor to Galpha 11 requires both beta/gamma interactions and an aromatic group four amino acids from the C terminus of the G protein.

Co-expression of the alpha(1b)-adrenoreceptor and Galpha(11) in cells derived from a Galpha(q)/Galpha(11) knock-out mouse allows agonist-mediated elevation of intracellular Ca(2+) levels that is transduced by beta/gamma released from the G protein alpha subunit. Mutation of Tyr(356) of Galpha(11) to Phe, within a receptor contact domain, had little effect on function but this was reduced greatly by alteration to Ser and virtually eliminated by conversion to Asp. This pattern was replicated following incorporation of each form of Galpha(11) into fusion proteins with the alpha(1b)-adrenoreceptor. Following a [(35)S]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding assay, immunoprecipitation of the wild type alpha(1b)-adrenoreceptor-Galpha(11) fusion protein indicated that the agonist phenylephrine stimulated guanine nucleotide exchange on Galpha(11) more than 30-fold. Information transfer by agonist was controlled in residue 356 Galpha(11) mutants with rank order Tyr > Phe > Trp > Ile > Ala = Gln = Arg > Ser > Asp, although these alterations did not alter the binding affinity of either phenylephrine or an antagonist ligand. Mutation of a beta/gamma contact interface in the alpha(1b)-adrenoreceptor-Tyr(356) Galpha(11) fusion protein did not alter ligand binding affinity but did reduce greatly beta/gamma binding and phenylephrine stimulation of [(35)S]GTPgammaS binding. It also prevented agonist elevation of intracellular Ca(2+) levels, as did a mutation in Galpha(11) that prevents G protein subunit dissociation. These results indicate that a bulky aromatic group is required four amino acids from the C terminus of Galpha(11) to maximize information transfer from an agonist-occupied receptor and disprove the hypothesis that tyrosine phosphorylation of this residue is required for G protein activation (Umemori, H., Inoue, T., Kume, S., Sekiyama, N., Nagao, M., Itoh, H., Nakanishi, S., Mikoshiba, K., and Yamamoto, T. (1997) Science 276, 1878-1881). This is distinct from Galpha(i1), where hydrophobicity of the amino acid is the key determinant at this location. They also further demonstrate a key role for the beta/gamma complex in enhancing receptor to G protein alpha subunit information transfer.

Selectivity in the oligomerisation of G protein-coupled receptors.

G protein-coupled receptors can exist as dimers and/or higher order oligomers. Such quaternary structure appears central to their plasma membrane delivery and, potentially, to function. Recent evidence that these receptors can form hetero- as well as homo-dimers/oligomers has significant implications for pharmacology and pathophysiology. Knowledge of the basis and selectivity of GPCR hetero-dimerisation is thus vital. Current understanding of these areas is reviewed.

Domain swapping in the human histamine H1 receptor.

G-protein-coupled receptors (GPCRs) represent the largest family of receptors involved in transmembrane signaling. Although these receptors were generally believed to be monomeric entities, accumulating evidence supports the presence of GPCRs in multimeric forms. Here, using immunoprecipitation as well as time-resolved fluorescence resonance energy transfer to assess protein-protein interactions in living cells, we unambiguously demonstrate the occurrence of dimerization of the human histamine H(1) receptor. We also show the presence of domain-swapped H(1) receptor dimers in which there is the reciprocal exchange of transmembrane domain TM domains 6 and 7 between the receptors present in the dimer. Mutation of aspartate(107) in transmembrane (TM) 3 or phenylalanine(432) in TM6 to alanine results in two radioligand-binding-deficient mutant H(1) receptors. Coexpression of H(1)D(107) A and H(1)F(432)A, however, results in a reconstituted radioligand binding site that exhibits a pharmacological profile that corresponds to the wild-type H(1) receptor. Interestingly, the H(1) receptor radioligands [(3)H]mepyramine and [(3)H]-(-)-trans-1-phenyl-3-N,N-dimethylamino-1,2,3,4-tetrahydronaphthalene show differential saturation binding values (B(max)) for wild-type H(1) receptors but not for the radioligand binding site that is formed upon coexpression of H(1) D(107)A and H(1) F(432)A receptors, suggesting the presence of different H(1) receptor populations.