Protein kinases, calmodulin-associated

Most protein serine-threonine kinases undergo autophosphorylation. The autophosphorylation of most protein kinases is associated with an increase in kinase activity [4, 10]. In some instances, such as with the RII subunit of PKA, autophosphorylation represents a positive feedback mechanism for kinase activation, in this case by enhancing the rate of dissociation of the RII and C subunits. In the case of CaMKII, autophosphorylation causes the catalytic activity of the enzyme to become independent of Ca2+ and calmodulin. This means that the enzyme, activated originally in response to elevated cellular Ca2+, remains active after Ca2+ concentrations have returned to baseline. By this mechanism, neurotransmitters that activate CaMKII can produce relatively long-lived alterations in neuronal function. In other instances, such as with the receptor-associated protein tyrosine kinases (discussed in Ch. 24), autophosphorylation is an obligatory step in the sequence of molecular events through which those kinases are activated and produce physiological effects. 

Currie, S., Loughrey, C. M., Craig, M. A., and Smith, G. L. (2004). Calcium/Calmodulin-Dependent Protein Kinase Ildelta Associates with the Ryanodine Receptor Complex and Regulates Channel Function in Rabbit Heart. Biochem J 377(Pt 2) 357-66. 

Bagni, C., Mannucci, L., Dotti, C. G., and Amaldi, F. (2000). Chemical stimulation of synaptosomes modulates alpha —Ca2+/calmodulin-dependent protein kinase II mRNA association to polysomes. J. Neurosci. 20, RC76. 

Ca2+,calmodulin-dependent May transiently associate with synaptic vesicles to phosphorylate synapsins and rabphilin-3A. May regulate various protein kinases I and II steps in neurotransmitter release. 

The cAMP and Ca2+ pathways also interact at the level of protein kinases and protein phosphatases. This is illustrated by inhibitor-1 and DARPP-32, which are phosphorylated and activated by PKA and then inhibit PP1, which can dephosphorylate numerous substrates for Ca2+-dependent protein kinases. Another example is the physical association between PKA and PP2B (a Ca2+/ calmodulin-activated enzyme) via the AKAP-anchoring proteins. 

DG). InsP3, as we saw above, stimulates the release of Ca2+, sequestered in the ER, and this in turn activates numerous cellular processes through Ca2+-binding proteins, such as calmodulin. The membrane-associated DG activates protein kinase C to phosphorylate and activate other enzymes, such as glycogen phosphorylase. This step also requires Ca2+. 

The calcium mediated contraction of smooth muscle, which unlike striated muscle does not contain troponin, is quite different and requires a particular calcium-binding protein called calmodulin. Calmodulin (CM) is a widely distributed regulatory protein able to bind, with high affinity, four Ca2+ per protein molecule. The calcium—calmodulin (CaCM) complex associates with, and activates, regulatory proteins, usually enzymes, in many different cell types in smooth muscle the target regulatory proteins are caldesmon (CDM) and the enzyme myosin light chain kinase (MLCK). As described below, CaCM impacts on both actin and myosin filaments. 

This enzyme [EC 2.7.1.123], also referred to as calcium/ calmodulin-dependent protein kinase type II, and micro-tubule-associated protein MAP2 kinase, catalyzes the reaction of ATP with a protein to produce ADP and an 0-phosphoprotein. The enzyme requires calcium ions and calmodulin. Proteins that can serve as substrates include vimentin, synapsin, glycogen synthase, the myosin light-chains, and the microtubule-associated tau protein. This enzyme is distinct from myosin light-chain kinase [EC 2.7.1.117], caldesmon kinase [EC 2.7.1.120], and tau-protein kinase [EC 2.7.1.135]. 

An example for the reversible association of activator proteins with an enzyme is the Ca -calmodulin dependent enzymes. Calmodulin is a Ca -binding protein which can activate target enzymes, e.g. phosphorylase kinase (see 6.7.1 and 7.4) in its Ca -boimd form. Another example for activating proteins is the cyclins (see chapter 14). The cyc-lins are activators of protein kinases that regulate the cell cycle. 

The amino-terminal domain is on the left the carboxyl-terminal domain on the right, (b) Calmodulin associated with a helical domain (red) of one of the many enzymes it regulates, calmodulin-dependent protein kinase II (PDB ID 1CDL). Notice that the long central a helix visible in (a) has bent back on itself in binding to the helical substrate domain. The central helix is clearly more flexible in solution than in the crystal, (c) Each of the four Ca2+-binding sites occurs in a helix-loop-helix motif called the EF hand, also found in many other Ca2+-binding proteins. 

In primary cultures of neonatal cerebellar granule neurons, all Ca2+ sensors, calmodulin, protein kinases C (PKC), and the p21(ras)/phosphatidylinositol 3 -kinase (Ptdlns-3K)/Akt pathway, converge towards NF-kB at the levels of nuclear translocation as well as transcription. The duration of NF-kB activation is a critical determinant for sensitivity toward excitotoxic stress and is dependent on the different upstream and downstream signaling associated with various kinases. This is in contrast to studies in non-neuronal cells, which either do not respond to Ca2+ or do not simultaneously activate all three cascades (Lilienbaum and Israel, 2003). Collective evidence suggests that brain inflammatory processes differ from systemic inflammation not only in the involvement of various types of neural cells but also in differences in response to second messengers. 

Baudier J, Mochly-Rosen D, Newton A, Lee SH, Koshland DE, Jr., Cole RD. 1987. Comparison of SlOOb protein with calmodulin interactions with melittin and microtubule-associated tau proteins and inhibition of phosphorylation of tau proteins by protein kinase C. Biochemistry 26(10) 2886-2893. 

Yokokura, H., Picciotto, M. R., Naim, A. C. and Hidaka, H., 1995, The regulatory region of calcium/calmodulin-dependent protein kinase I contains closely associated autoinhibitory and calmodulin-binding domains, J Biol Chem, 270, pp 23851—9. 

Benfenati F, Valtorta F, Rubenstein JL et al (1992b) Synaptic vesicle-associated Ca2+/calmodulin-dependent protein kinase II is a binding protein for synapsin I. Nature 359 417-20 Benians A, Nobles M, Hosny S et al (2005) Regulators of G-protein signaling form a quaternary complex with the agonist, receptor, and G-protein. A novel explanation for the acceleration of signaling activation kinetics. J Biol Chem 280 13383-94... 

Zhang, T., Johnson, E.N., Gu, Y., Morissette, M.R., Sah, V.P., Gigena, M.S., Belke, D.D., Dillman, W.H., Rogers, T.B., Schulman, H., Ross, J., Jr., and Brown, J.H. 2002. The cardiac-specific nuclear 6b isoform of Ca2+/calmodulin dependent protein kinase II induces hypertrophy and dilated cardiomyopathy associated with increased protein phosphatase 2A activity. J. Biol. Chem. 277 1261-1267. 

Martin-Padura I, Lostaglio S, Schneemann M, LW, Romano M, Fruscella P, Panzeri C, Stoppacciaro A, Ruco L, Villa A, Simmons D, Dejana E (1998) Junctional adhesion molecule, a novel member of the immunoglobulin superfamily that distributes at intercellular junctions and modulates monocyte transmigration. J Cell Biol 142 117-127 Martinez-Estrada OM, Villa A, Breviario F, Orsenigro F, Dejana E, Bazzoni G (2001) Association of junctional adhesion molecule with calcium/calmodulin-dependent serine protein kinase (CASK/LIN-2) in human epithelial Caco-2 cells. J Biol Chem 276 9291-9296... 

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