Switch‖l Switch I Figure 15.3 The structure of a G protein and the G pror cycle. la) Comparison of the tertiary strictire nf the anti
(3)Binding domains and their recognized motifs in intracellular signaling protein signal molecule receptor phospholipid protein PTB SH2P) CYTOSOL naling protein 1 signaling protein 2 kinase domain SH2 adaptor protein SH3 signaling protein 3 RELAYS SIGNAL DOWNSTREAM BINDING DOMAIN MOTIF RECOGNIZED PH= Pleckstrin homology domain phosphorylated inositol phospholipid PTB= phosphotyrosine-binding domain SH2= Src homology 2 domain Y s phosphotyrosine SH3- Src homology 3 domain PPL= proline-rich motif
(3) Binding domains and their recognized motifs in intracellular signaling protein
(4) Epinephrin 10-10M Amplification △ Adenylyl Amplification AMP 10-6 M Ki Amplification Activated enzyme Amplification Product A FIGURE 20-37 Intracellular transduction of an extracellular ignal via a cascade of sequential reactions produces a large amplification of the signal. In this example, binding of a single epinephrine molecule to one receptor molecule induces synthesis of a large number of cAMP molecules. These in turn activate multiple enzyme molecules, each of which produces multiple product molecules (e. g, active phosphorylated proteins).The more steps in such a cascade, the greater the signal amplification possible
(4)
4. Receptors he target cell responds to signaling molecule by means of a specific protein called a receptor, which specifically binds the signalin g molecule from the signaling cell with high affinity(Ka>108 liters/mole, ligand conc. < 10-8M) and then initiates a response in the target cell There are two kinds of receptors, which are either on cell-surface or inside the cell for signaling molecules (ligands)
4.Receptors The target cell responds to signaling molecule by means of a specific protein called a receptor, which specifically binds the signaling molecule from the signaling cell with high affinity (Ka > 108 liters/mole, ligand conc. < 10-8 M ) and then initiates a response in the target cell. There are two kinds of receptors, which are either on cell-surface or inside the cell for signaling molecules (ligands)
1)受体的基本性质 并不是所有能与胞外物质或信号分子结合的膜蛋白都是受体。 作为受体具有如下基本特征: (1)特异性,受体的结合部位的立体构象具有高度的选择性, 能够准确识别并特异地结合(可以是诱导嵌合)结构上互补的 配体分子,一种受体仅能与一种配体特异结合。(2)高亲和性, 配体表观解离常数Ka值通常在10-9M~10-12M之间。(3)饱和 特性,配体与受体达到最大值结合后,结合不再随配体浓度的 增大而增加。(4)结合是可逆的,配体与受体复合物可以被解 离。(5)可以发生竞争性抑制。(6)受体在外部信号作用下, 能够在细胞膜内侧或胞内产生新的信号或第二信使,使信号得 以放大并通过级联反应途径产生相应的生理效应。 从技术角度上细胞膜表面受体可以看成具有分子识别功能的 生物传感器,它组装在细胞膜基片上。各种受体的化学本质均 以蛋白质为主体,其中许多是糖蛋白。例如,肾上腺素能β受体 结构有7个跨膜螺旋,受体在膜两侧的短的环状片段把跨膜片段 连接起来,胞外片段与配体特殊结合,引起胞内部分构象变化 并结合和激活信号介导分子。作为一个分子传感器,细胞
1) 受体的基本性质 并不是所有能与胞外物质或信号分子结合的膜蛋白都是受体。 作为受体具有如下基本特征： （1）特异性，受体的结合部位的立体构象具有高度的选择性， 能够准确识别并特异地结合（可以是诱导嵌合）结构上互补的 配体分子，一种受体仅能与一种配体特异结合。（2）高亲和性， 配体表观解离常数Ka值通常在10－9M～10－12M之间。（3）饱和 特性，配体与受体达到最大值结合后，结合不再随配体浓度的 增大而增加。（4）结合是可逆的，配体与受体复合物可以被解 离。（5）可以发生竞争性抑制。（6）受体在外部信号作用下， 能够在细胞膜内侧或胞内产生新的信号或第二信使，使信号得 以放大并通过级联反应途径产生相应的生理效应。 从技术角度上, 细胞膜表面受体可以看成具有分子识别功能的 生物传感器，它组装在细胞膜基片上。各种受体的化学本质均 以蛋白质为主体，其中许多是糖蛋白。例如，肾上腺素能β受体 结构有7个跨膜螺旋，受体在膜两侧的短的环状片段把跨膜片段 连接起来，胞外片段与配体特殊结合，引起胞内部分构象变化 并结合和激活信号介导分子。作为一个分子传感器，细胞