Protein activity regulation

A receptor is a surface membrane component, usually a protein, which regulates some biological event in response to reversible binding of a relatively small molecule40 . The precise three-dimensional structures of the binding sites of receptors still remain unknown today. Thus, this section mainly describes the correlation of shape similarity between the molecules which would bind to a given receptor with their biological activity. 

Phosphorylation by protein kinases of specific seryl, threonyl, or tyrosyl residues—and subsequent dephosphorylation by protein phosphatases—regulates the activity of many human enzymes. The protein kinases and phosphatases that participate in regulatory cascades which respond to hormonal or second messenger signals constimte a bio-organic computer that can process and integrate complex environmental information to produce an appropriate and comprehensive cellular response. 

Figure 39-17. Proteins that regulate transcription have several domains. This hypothetical transcription factor has a DNA-binding domain (DBD) that is distinct from a ligand-binding domain (LBD) and several activation domains (ADs) (1-4). Other proteins may lack the DBD or LBD and all may have variable numbers of domains that contact other proteins, including co-regulators and those of the basal transcription complex (see also Chapters 42 and 43).

Other HIV proteins include regulator of viral expression (Rev), negative effectors (Nef), viral protein R (Vpr), viral protein U (Vpu), viral infectivity factor (Vif) and transactivator protein (Tat). These proteins are instrumental in viral mRNA expression, viral replication and transactivation, viral release and maturation, viral infection, and maintenance of viral transcript activation and expression, respectively (Tripathi and Agrawal 2007). 

Knall C, Worthen GS, Johnson GL. Interleukin 8-stimulated phosphatidylinositol-3-kinase activity regulates the migration of human neutrophils independent of extracellular signal-regulated kinase and p38 mitogen-activated protein kinases. Proc Natl Acad Sci U S A 1997 94(7) 3052-3057. 

Booher, R., and Beach, D. (1986). Site-specific mutagenesis of cdc2+, a cell cycle control gene of the fission yeast Schizosaccaromyces pombe. Mol. Cell. Biol. 6 3523-3530. Booher, R. N., Alfa, C. E., Hyams, J. S., and Beach, D. H. (1989). The fission yeast cdc2/cdcl3/sucl protein kinase regulation of catalytic activity and nuclear localization. CeU 58 485-497. 

Chen Y, Yu L. Differential regulation by cAM P-dependent protein kinase and protein kinase C of the k opioid receptor coupling to a G protein-activated K+ channel. J Biol Chem 1994 269 7839-7842. 

Yao I, Takagi H, Ageta H, et al. SCRAPPER-dependent ubiquitination of active zone protein RIM1 regulates synaptic vesicle release. Cell 2007 130 943-957. 

FIGURE 14-6 Main signaling pathways for histamine receptors. Histamine can couple to a variety of G-protein-linked signal transduction pathways via its four different receptors. The Hj receptor activates the phosphatidylinositol turnover via Gq/11 proteins. The other receptors either positively (H2 receptor) or negatively (H3 and H4 receptor) regulate adenylyl cyclase activity via Gs and GUo protein activation respectively. Several additional signaling pathways have been described, which are not shown. Abbreviations PfP2, phosphatidylinositol 4,5-bisphosphate PIC, phospholipase C AC, adenylyl cyclase ATP, adenosine triphosphate cAMP, cyclic AMP PKC, protein kinase C PICA, protein kinase A. 

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