GPCRs整合膜蛋白的一个家庭有7个membrane-spanning域和都与一个不活跃的G蛋白。一般来说,GPCRs是细胞表面受体的类型有关当讨论non-genomic甾类激素的行动。绑定的甾类激素GPCR导致受体的构象变化最终激活G蛋白。不活跃的G蛋白包含三个子单元:Gα,GβGγ。当激素结合GPCR,Gα子单元结合一个分子深受三磷酸鸟苷和与其他子单元。这样的激活G蛋白,因为它让网站在蛋白质暴露,这样其他分子可以很容易地与之交互。然后激活G蛋白启动信号从腺苷酸环化酶等效应的蛋白质和磷脂酶c .第二信使如环腺苷酸(cAMP),三磷酸肌醇(IP3),甘油二酯(DAG)和钙(2 +)离子被释放。
关键路径涉及营工作主要是通过激活蛋白激酶A(PKA)使用ATP作为底物磷酸化丝氨酸或苏氨酸残基的各种蛋白质在代谢途径激活或取消激活酶积分,同时涉及IP3的途径和DAG通过一系列更复杂的反应。(马歇尔布鲁克c和n . 1996)。磷脂磷脂酰肌醇4酮糖(PIP2)裂解生产DAG和IP3的磷脂酶C细胞上的DAG膜相关蛋白激酶C有类似效果的营地,其他蛋白质的磷酸化水平上升导致细胞活动。
There are two major groups that the receptors can be divided into; cell surface receptors and intracellular receptors. The cell surface receptors are transmembrane proteins integrated into the membrane which enables them to recognise various signalling molecules. Within the cell surface receptor group, there is a subdivision for the two main classes of cell surface receptors. These are that of G-protein coupled receptors (GPCRs) and receptors with a single transmembrane domain.
GPCRs are a family of integral membrane proteins which have seven membrane-spanning domains and are linked to an inactive G protein. Generally, GPCRs are the type of cell surface receptor concerned when discussing non-genomic steroid hormone action. The binding of a steroid hormone to a GPCR causes the conformation of the receptor to change which ultimately activates G protein. The inactive G protein consists of three subunits: Gα, Gβ and Gγ. When the hormone binds the GPCR, the Gα subunits binds one molecule of GTP and dissociates from the other subunits. This activates the G protein as it leaves sites on the protein exposed so that other molecules can readily interact with it. The activated G protein then initiates signalling from effector proteins such as adenylate cyclase and phospholipase C. Second messengers such as cyclic-AMP (cAMP), inositol triphosphate (IP3), diacylglycerol (DAG) and Calcium (2+) ions are then released.
The key pathway involving cAMP works primarily by activating protein kinase A (PKA) which uses ATP as a substrate to phosphorylate serine or threonine residues of various proteins that go on to activate or deactivate enzymes integral to metabolic pathways, whilst the pathway involving IP3 and DAG works by a more complex series of reactions. (Brook C. and Marshall N. 1996). Phospholipid phosphatidylinositol 4, 5-bisphophate (PIP2) is cleaved to produces DAG and IP3 by phospholipase C. The DAG on the cell membrane-associated protein kinase C has similar effects to those of increased levels of cAMP where phosphorylation of other proteins causes cellular activity.