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1、D103 - Cell Biology - lecture 19, 2011 Grant MacGregor e.g. by masking / unmasking of amino acid motifs. Control of steady-state level of protein; e.g. by poly-ubiquitination and degradation. Control ofspecificityof subcellular signaling; e.g. by scaffold proteins. Control of signaling protein activ
2、ity by proteolysis (i.e. cleavage, not degradation). Control of signaling response by positive and negative feedback. Amplification of signals and intracellular transduction of signal via small molecules (second messengers). Use of GTPases as timers to control signaling. Use of wide range of functio
3、nal domains (i.e. a region of conserved amino acid sequences) within different proteins. Enabling sophistication and functional redundancy inpathways, by duplication and divergence of geneswhose products areinvolved in signaling.,D103 - Cell Biology - lecture 19,D103 - Cell Biology - lecture 19, 201
4、1 Grant MacGregor & Christine Stterlin - all rights reserved,Intracellular signaling networks often use feedback loops to regulate activity,eg - use of positive feedback to mediate a rapid large scale increase in activity of an enzyme in presence of similar steady-state level of ligand,D103 - Cell B
5、iology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Intracellular mediators and enzymatic cascades amplify extracellular signals,Molecules must have short lifetimeto enable cellular machinery to change the concentration of a molecule to effect a rapid response to a s
6、ignal,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,A cell can alter the concentration of an intracellular molecule quickly only if the lifetime of the molecule is short (i.e. the molecule is turned over rapidly),(lifetime of molecule),D103 - Cell
7、Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Scaffolding proteins can provide specificity of signaling, and can facilitate negative feedback control of local concentration of cAMP,e.g. in b-adrenergic receptor mediated signaling in cardiac muscle,AKAP - A-Kin
8、ase (PKA) Anchoring Protein PDE - cAMP phosphodiesterase,Note - in panel 2, catalytic subunit (C) of PKA phosphorylates other target proteins (not shown),D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Cells can use negative feedback to adjust their
9、sensitivity to a signal,e.g. example of adjustment of signaling in photoreceptors (rods) following exposure to bright light,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Cells can use negative feedback to adjust their sensitivity to a signal,e.g. e
10、xample of adjustment of signaling in photoreceptors (rods) following exposure to bright light,In the absence of signaling from Gt in response to bright light, how can you see ? You cant - you are blind ! Different photoreceptors can compensate. The diagram is overtly simplistic - there is still suff
11、icient signaling in rods to enable perception of light. Signaling can occur via newly synthesized rhodopsin. b-Arrestins can still permit signaling.,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Cells can adjust their sensitivity to a signal - exam
12、ples of negative feedback of receptor signaling,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Notice how cross-talk can occur between different pathways at the level of the intracellular signal transduction machinery,Most activated cell surface rec
13、eptors relay signals via small molecules and networks of intracellular signaling proteins,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Crosstalk and redundant pathways facilitate sophistication in signaling,A relatively small number of signaling s
14、ystems formsa core toolbox. Each system is used repeatedly in different organisms, in different tissues, at different times, in response to different signals. Enables sophisticated signaling with small numbers of components. Gene duplication and divergence has led to specialization of individual com
15、ponents of a signaling system. Redundancy and overlap in signaling pathways offers opportunities for evolution of novel signaling pathways.,There aremanyindependent pathways involving thousands of different proteins. We still havent identified all of the pathways. Simple linearpathways are rare. Mos
16、t pathways branch and converge, multiple times. Most pathways have positive or negative feedback loops that can result in signals being only transient in nature - makes them more difficult to study. Response of some pathways depends on both intensity and duration of signal. Requires advanced quantitative 4-D analytical methods to investigate.,D103 - Cell Biology - lecture 19, 2011 Grant MacGregor & Christine Stterlin - all rights reserved,Intracellular signaling complexes enhance speed and e
