RESUMO
Taste sensing is a sophisticated chemosensory process, and bitter taste perception is mediated by type 2 taste receptors (TAS2Rs), or class T G protein-coupled receptors. Understanding the detailed molecular mechanisms behind taste sensation is hindered by a lack of experimental receptor structures. Here, we report the cryo-electron microscopy structures of human TAS2R46 complexed with chimeric mini-G protein gustducin, in both strychnine-bound and apo forms. Several features of TAS2R46 are disclosed, including distinct receptor structures that compare with known GPCRs, a new "toggle switch," activation-related motifs, and precoupling with mini-G protein gustducin. Furthermore, the dynamic extracellular and more-static intracellular parts of TAS2R46 suggest possible diverse ligand-recognition and activation processes. This study provides a basis for further exploration of other bitter taste receptors and their therapeutic applications.
Assuntos
Neurotoxinas , Receptores Acoplados a Proteínas G , Estricnina , Paladar , Microscopia Crioeletrônica , Humanos , Ligantes , Neurotoxinas/farmacologia , Conformação Proteica , Receptores Acoplados a Proteínas G/agonistas , Receptores Acoplados a Proteínas G/química , Estricnina/farmacologia , Paladar/efeitos dos fármacosAssuntos
Apoproteínas/química , Receptores de Glutamato Metabotrópico/química , Apoproteínas/genética , Apoproteínas/metabolismo , Baculoviridae/genética , Baculoviridae/metabolismo , Sítios de Ligação , Carbamatos/química , Carbamatos/metabolismo , Clonagem Molecular , Microscopia Crioeletrônica , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Humanos , Modelos Moleculares , Mutação , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Multimerização Proteica , Ácido Quisquálico/química , Ácido Quisquálico/metabolismo , Receptores de Glutamato Metabotrópico/genética , Receptores de Glutamato Metabotrópico/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Anticorpos de Domínio Único/química , Anticorpos de Domínio Único/metabolismo , Xantenos/química , Xantenos/metabolismoRESUMO
Optimization of mechanical properties is required in applications of tissue-engineered scaffolds. In this study, a polyelectrolyte complexation approach is proposed to improve the mechanical properties of the nanofibrous scaffolds. Through an electrospun chitosan/gelatin (CG) model system, it is demonstrated that the storage modulus of CG nanofiber-based complex membranes is over 10(3)-fold higher than that of neat chitosan or gelatin membranes. Further, an annealing process was found to promote the conjugation of the oppositely charged polymers and thus the tensile modulus of CG membranes is 1.9-fold elevated. When the molar ratio of aminoglucoside units in chitosan to carboxyl units in gelatin is 1:1, the complex nanofiber-based membranes (CG2) display the highest mechanical strength. In addition, the complex membranes reveal an excellent swelling capacity. By comparing the CG membranes electrospun with cast, it is deduced that the complexation is one of the main contributing factors to the improvement in mechanical properties. FTIR and DSC analyses confirm that more molecular interactions took place in the complexation. SEM observation clearly displays the electrospinnability of the complex. Therefore, polyelectrolyte complexation is an effective strategy for enhancing mechanical properties of nanofibrous scaffolds. These mechanically enhanced chitosan/gelatin nanofibrous membranes have wider applications than wound dressing.
