Some Common Themes & Challenges of Signal Transduction Intracellular communication evolved to meet the challenges of: Specificity, Access & Deactivation Common Themes 1. Signal transduction pathways are turned ON by the arrival of a signal. 2. The involvement of a receptor a. Typically, ectodomains of transmembrane receptors bind impermeable ligands. b. Lipophilic signals that traverse the membrane are bound by intracellular receptors. 3. Modifications to existing molecules that involve making or breaking covalent bonds a. The action of kinases and phosphatases. b. Proteolytic cleavage. c. Covalent additions 4. The Generation of second messengers. There are many different second messengers and the list includes: a. Agents derived from membrane phospholipids (DAG, IP3, ceramide). b. Cyclic nucleotides (cAMP, cGMP) c. Ca+2 d. Gases (No in bacteria and eucaryotes; ethylene in plants) 5. Small and large G proteins 6.The induced assembly or targeted translocation of critical components of the signal transduction pathway. Many signal transduction pathways depend upon the induced assembly of critical components a. Protein-modified peptide (these include Phosphotyrosine/SH2 interactions) Protein –phospholipid (PH/PIP3 and many others) b. Protein-peptidyl motif (SH3/RXXK or SH3/PXXXP and many others) c. Protein domain-protein domain d. Adaptor proteins link different protein components into signaling complexes. 7. Cascades to amplify and relay signals 8. Compartmentation. 9. Signal transdution pathways interact with each other (‘crosstalk’ is the rule rather than the exception). 10. The default setting for signal transduction pathways is OFF
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