Signaling pathway General functions

Neurotrophins (NGF brain-derived neurotrophic factor, BDNF neurotrophin-3, NT-3 NT-4 NT-6) are important regulators of neural survival, development, function, and plasticity of the vertebrate nervous system [1]. Neurotrophins generally function as noncovalently associated homodimers. They activate two different classes of receptors, through which signaling pathways can be activated, including those mediated by Ras and members of the cdc42/rac/rho G protein families, MAP kinase, PI-3 kinase, and Jun kinase cascades. 

Fig. 5.5. General functions of transmembrane receptors. Extracellular signals convert the transmembrane receptor from the inactive form R to the active form R. The activated receptor transmits the signal to effector proteins next in the reaction sequence. Important effector reactions are the activation of heterotrimeric G-proteins, of protein tyrosine kinases and of protein tyrosine phosphatases. The tyrosine kinases and tyrosine phosphatases may be an intrinsic part of the receptor or they may be associated with the receptor. The activated receptor may also include adaptor proteins in the signaling pathway or it may induce opening of ion channels.

The protein kinase family encompasses more than three hundred members of critically important enzymes, each one with a specific role or function within the cell. These enzymes, ATP-phosphotransferases, recognize target proteins and through the phosphorylation of specific sites either activate or deactivate a particular pathway of signal transduction. Many of these signaling pathways are associated with cell surface receptors, which are located in the membranes that surround cells. The difference between the families of protein kinases is that they have different targets and generally fall into two major classes ... 

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