RESUMO
We have recently developed a mouse monoclonal antibody (12-10H) binding to the head domain region in rat P2X4 receptor (rP2X4R, which is crucial for the pathogenesis of neuropathic pain) expressed on the cell with the highest binding affinity (KD = 20 nM). However, the 12-10H antibody failed to detect endogenously expressed P2X4Rs in microglia isolated from the spinal cord of rats whose spinal nerves were injured. Then, we prepared R5 mutant, in which five arginine residues were introduced into variable regions except for the "hot spot" in the 12-10H antibody to increase electrostatic interactions with the head domain, an anionic region, in rP2X4R. The mutation resulted in an increase of 50-fold in the affinity of the R5 mutant for the head domain with respect to the intact 12-10H antibody. As a result, detection of P2X4Rs endogenously expressed on primary cultured microglial cells originated from the neonatal rat brain and spinal cord microglia isolated from a rat model of neuropathic pain was achieved. These findings suggest a strategy to improve the affinity of a monoclonal antibody for an anionic antigen by the introduction of several arginine residues into variable regions other than the "hot spot" in the paratope.
Assuntos
Anticorpos Monoclonais/farmacologia , Microglia/efeitos dos fármacos , Neuralgia/tratamento farmacológico , Antagonistas do Receptor Purinérgico P2X/farmacologia , Receptores Purinérgicos P2X4/efeitos dos fármacos , Animais , Anticorpos Monoclonais/imunologia , Afinidade de Anticorpos , Especificidade de Anticorpos , Células CHO , Linhagem Celular Tumoral , Cricetulus , Modelos Animais de Doenças , Humanos , Masculino , Microglia/imunologia , Microglia/metabolismo , Mutação , Neuralgia/imunologia , Neuralgia/metabolismo , Ligação Proteica , Conformação Proteica , Antagonistas do Receptor Purinérgico P2X/imunologia , Ratos Wistar , Receptores Purinérgicos P2X4/genética , Receptores Purinérgicos P2X4/imunologia , Receptores Purinérgicos P2X4/metabolismo , Eletricidade Estática , Relação Estrutura-AtividadeRESUMO
P2X purinergic receptors are ATP-driven ionic channels expressed as trimers and showing various functions. A subtype, the P2X4 receptor present on microglial cells is highly involved in neuropathic pain. In this study, in order to prepare antibodies recognizing the native structure of rat P2X4 (rP2X4) receptor, we immunized mice with rP2X4's head domain (rHD, Gln111-Val167), which possesses an intact structure stabilized by S-S bond formation (Igawa and Abe et al. FEBS Lett. 2015), as an antigen. We generated five monoclonal antibodies with the ability to recognize the native structure of its head domain, stabilized by S-S bond formation. Site-directed mutagenesis revealed that Asn127 and Asp131 of the rHD, in which combination of these amino acid residues is only conserved in P2X4 receptor among P2X family, were closely involved in the interaction between rHD and these antibodies. We also demonstrated the antibodies obtained here could detect rP2X4 receptor expressed in 1321N1 human astrocytoma cells.
