Cells expressing recombinant wild-type receptors but not control CHO-K1 cells (Fig. 2). Normal serum IgG from non-immunized mice, used as control, bound neither to wild type CHO-K1 cells nor to GPCRexpressing cells (Fig. 2c). The ability of anti-hNPFFR2 IgG to discriminate receptors with high amino acid sequence homology was evaluated by cytofluorometry. Although hNPFFR2 receptors originating from human, mouse and rat display more than 77 amino acid sequence identity [34] (Fig. 4), anti-hNPFFR2 antibodies only bound to human NPFFR2 that has been used to immunized animals (Fig. 3b). Similar 
results were obtained in western-blotting experiments (Fig. 3c). Thus, the anti-GPCR antibodies produced by using full-length GPCR molecules as immunogens, display a strong discriminative potency that allows them to distinguish between structurally similar molecules. Moreover, as exemplified with 4 IBP MedChemExpress 14636-12-5 Anti-hMOR antibodies that recognize the full-length but not the NH2 terminal-truncated form of the hMOR (Fig. 3d), antibodies might rather recognize extracellular domains of GPCRs.assessed by western-blotting on protein extracts from human spermatozoa, anti-hMOR as well as anti-hKOR serum IgG antibodies (dilution 1/2000) revealed only one band at the expected molecular weight (Fig. 5a). No band was revealed with control serum IgG from normal non-immunized mice used at the same dilution (Fig. 5a). Anti-hMOR serum IgG also revealed receptors endogenously expressed in SH-SY5Y neuroblastoma cells as assessed by immunocytofluorescence (Fig. 5b). AntihMOR antibody staining of SH-SY5Y neuroblastoma cells, revealed receptors expressed within the cytoplasm rather than at the membrane cell surface. This cellular distribution 
of MOR that contrasts with that observed in hMOR-expressing CHO cells was previously described in neurons [38]. The expression level of MOR in SH-SY5Y cells was then determined by using the MORselective opioid ligand [D-Ala2, N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO). Binding assays performed on proteins extracted from crude membrane preparations including membranes from organelles, indicated that anti-hMOR IgG antibodies may detect receptors expressed at 0.04 pmol/mg of membrane proteins. As shown in figure 5c, anti-hMOR antibodies did not exhibit crossreactivity towards mouse tissue extracts including MOR-expressing tissue such as olfactory bulb and cerebellum.DiscussionOur data indicate that immunization with functional native-like GPCRs is not required to generate 15755315 specific antibodies able to recognize GPCRs in both native and denaturated forms. AntiGPCR antibodies generated against SDS-solubilized or lyophilized proteins recognize native receptors expressed at the membrane surface of living cells (cytofluorometry) as well as denaturated/unfolded receptors (western-blotting and confocal microscopy). The antigen-binding site of antibodies may be conformational (i.e. dependent on receptor folding) or linear (i.e. dependent on primary sequence). Contrasting with linear epitopes that are exposed on unfolded receptor, conformational antigenic determinants accessible on native receptor are usually lost upon denaturation. However, as we have previously shown for MOR [39,40], SDS-solubilized GPCRs display true helical secondary structures. SDS-solubilized GPCRs are probably not fully unfolded, but rather partially pre-folded, at least as far as the secondary structure is considered [26]. Alternatively, it could be hypothesized that n-alkanes (mineral oil).Cells expressing recombinant wild-type receptors but not control CHO-K1 cells (Fig. 2). Normal serum IgG from non-immunized mice, used as control, bound neither to wild type CHO-K1 cells nor to GPCRexpressing cells (Fig. 2c). The ability of anti-hNPFFR2 IgG to discriminate receptors with high amino acid sequence homology was evaluated by cytofluorometry. Although hNPFFR2 receptors originating from human, mouse and rat display more than 77 amino acid sequence identity [34] (Fig. 4), anti-hNPFFR2 antibodies only bound to human NPFFR2 that has been used to immunized animals (Fig. 3b). Similar results were obtained in western-blotting experiments (Fig. 3c). Thus, the anti-GPCR antibodies produced by using full-length GPCR molecules as immunogens, display a strong discriminative potency that allows them to distinguish between structurally similar molecules. Moreover, as exemplified with anti-hMOR antibodies that recognize the full-length but not the NH2 terminal-truncated form of the hMOR (Fig. 3d), antibodies might rather recognize extracellular domains of GPCRs.assessed by western-blotting on protein extracts from human spermatozoa, anti-hMOR as well as anti-hKOR serum IgG antibodies (dilution 1/2000) revealed only one band at the expected molecular weight (Fig. 5a). No band was revealed with control serum IgG from normal non-immunized mice used at the same dilution (Fig. 5a). Anti-hMOR serum IgG also revealed receptors endogenously expressed in SH-SY5Y neuroblastoma cells as assessed by immunocytofluorescence (Fig. 5b). AntihMOR antibody staining of SH-SY5Y neuroblastoma cells, revealed receptors expressed within the cytoplasm rather than at the membrane cell surface. This cellular distribution of MOR that contrasts with that observed in hMOR-expressing CHO cells was previously described in neurons [38]. The expression level of MOR in SH-SY5Y cells was then determined by using the MORselective opioid ligand [D-Ala2, N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO). Binding assays performed on proteins extracted from crude membrane preparations including membranes from organelles, indicated that anti-hMOR IgG antibodies may detect receptors expressed at 0.04 pmol/mg of membrane proteins. As shown in figure 5c, anti-hMOR antibodies did not exhibit crossreactivity towards mouse tissue extracts including MOR-expressing tissue such as olfactory bulb and cerebellum.DiscussionOur data indicate that immunization with functional native-like GPCRs is not required to generate 15755315 specific antibodies able to recognize GPCRs in both native and denaturated forms. AntiGPCR antibodies generated against SDS-solubilized or lyophilized proteins recognize native receptors expressed at the membrane surface of living cells (cytofluorometry) as well as denaturated/unfolded receptors (western-blotting and confocal microscopy). The antigen-binding site of antibodies may be conformational (i.e. dependent on receptor folding) or linear (i.e. dependent on primary sequence). Contrasting with linear epitopes that are exposed on unfolded receptor, conformational antigenic determinants accessible on native receptor are usually lost upon denaturation. However, as we have previously shown for MOR [39,40], SDS-solubilized GPCRs display true helical secondary structures. SDS-solubilized GPCRs are probably not fully unfolded, but rather partially pre-folded, at least as far as the secondary structure is considered [26]. Alternatively, it could be hypothesized that n-alkanes (mineral oil).
