Carbonyl{3,3′-di-tert-butyl-5,5′-dimethoxy-2,2′-bis[(4,4, 5,5-tetramethyl-1,3,2-dioxaphospholan-2-yl)oxy]biphenyl-κ2 P,P′}hydrido(triphenylphosphane-κP)rhodium(I) diethyl ether trisolvate

In the title compound, [RhH(C74H68O8P2)(C18H15P)(CO)]·3C4H10O, the CHP3 coordination set at the RhI ion is arranged in a distorted trigonal-bipyramidal geometry with the P atoms adopting equatorial coordination sites and the C atom of the carbonyl ligand as well as the H atom adopting the axial sites. The asymmetric unit contains two very similar molecules of the rhodium complex, two half-occupied diethyl ether molecules and further diethyl ether solvent molecules which could not be modelled successfully. Therefore contributions of the latter were removed from the diffraction data using the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148-155]

Electronic sculpting of ligand-GPCR subtype selectivity:the case of angiotensin II

GPCR subtypes possess distinct functional and pharmacological profiles, and thus development of subtype-selective ligands has immense therapeutic potential. This is especially the case for the angiotensin receptor subtypes AT1R and AT2R, where a functional negative control has been described and AT2R activation highlighted as an important cancer drug target. We describe a strategy to fine-tune ligand selectivity for the AT2R/AT1R subtypes through electronic control of ligand aromatic-prolyl interactions. Through this strategy an AT2R high affinity (<i>K</i>_i = 3 nM) agonist analogue that exerted 18,000-fold higher selectivity for AT2R versus AT1R was obtained. We show that this compound is a negative regulator of AT1R signaling since it is able to inhibit MCF-7 breast carcinoma cellular proliferation in the low nanomolar range

Examining the effects of sodium ions on the binding of antagonists to dopamine D2 and D3 receptors

Many G protein-coupled receptors have been shown to be sensitive to the presence of sodium ions (Na+). Using radioligand competition binding assays, we have examined and compared the effects of sodium ions on the binding affinities of a number of structurally diverse ligands at human dopamine D2 and dopamine D3 receptor subtypes, which are important therapeutic targets for the treatment of psychotic disorders. At both receptors, the binding affinities of the antagonists/inverse agonists SB-277011-A, L,741,626, GR 103691 and U 99194 were higher in the presence of sodium ions compared to those measured in the presence of the organic cation, N-methyl-D-glucamine, used to control for ionic strength. Conversely, the affinities of spiperone and (+)-butaclamol were unaffected by the presence of sodium ions. Interestingly, the binding of the antagonist/inverse agonist clozapine was affected by changes in ionic strength of the buffer used rather than the presence of specific cations. Similar sensitivities to sodium ions were seen at both receptors, suggesting parallel effects of sodium ion interactions on receptor conformation. However, no clear correlation between ligand characteristics, such as subtype selectivity, and sodium ion sensitivity were observed. Therefore, the properties which determine this sensitivity remain unclear. However these findings do highlight the importance of careful consideration of assay buffer composition for in vitro assays and when comparing data from different studies, and may indicate a further level of control for ligand binding in vivo

Dicarbonyl-{3,3′-di-tert-butyl-5,5′-di-methoxy-2, 2′-bis[(4,4,5,5-tetraphenyl-1,3,2-dioxaphospho-lan-2-yl)-oxy-κP] biphen-yl}hydridorhodium(I) diethyl ether monosolvate

In the title compound, [Rh(C 74H 68O 8P2)H(CO) 2]·C 4H 10O, the C 2HP 2 coordination set at the Rh I ion is arranged in a distorted trigonal-planar geometry with one P atom of the diphosphite mol-ecule and the H atom adopting the axial coordination sites

Effects of palmitoylation of Cys 415 in helix 8 of the CB1 cannabinoid receptor on membrane localization and signalling

Background and purpose:  The CB(1) cannabinoid receptor is regulated by its association with membrane microdomains like the lipid rafts. Here we investigated the role of CB(1) palmitoylation by analyzing the functional consequences of site-specific mutation of cysteine 415, the likely palmitoylated residue at the end of helix 8, in terms of membrane association, raft targeting and signalling of the receptor. Experimental approach:  The palmitoylation state of the CB(1) receptor was assessed in rat forebrain by depalmitoylation/repalmitoylation experiments. Cysteine 415 was replaced with alanine by site directed mutagenesis. Green fluorescence protein chimeras of both wild-type and mutant receptors were transiently expressed and functionally characterised in SH-SY5Y cells and HEK-293 cells by means of confocal microscopy, cytofluorimetry and competitive binding assays. Confocal FRAP was used to assess receptor membrane dynamics, whereas [(35) S]GTPγS, cAMP and co-immunoprecipitation assays were employed to assess signalling activity. Key results:  Endogenous CB(1) receptors were palmitoylated in rat brain. Mutation of cysteine 415 in transfected cells prevented the palmitoylation of the receptor and significantly reduced it recruitment at both plasma membrane and lipid rafts; it also increased protein diffusional mobility. The same mutation markedly reduced the functional coupling of CB(1) receptor with G proteins and adenylyl cyclase, whereas depalmitoylation abrogated receptor association with a specific subset of G proteins. Conclusions and implications:  We found that CB(1) receptor is post-translationally modified by palmitoylation and that mutation of cysteine 415 gives rise to a form of receptor that is functionally impaired in terms of membrane targeting and signalling.[...