scholarly journals The CaMKII holoenzyme structure in activation-competent conformations

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Janette B. Myers ◽  
Vincent Zaegel ◽  
Steven J. Coultrap ◽  
Adam P. Miller ◽  
K. Ulrich Bayer ◽  
...  
Keyword(s):  
Molecular Crowding ◽  
Extended State ◽  
Dependent Protein Kinase ◽  
Subunit Exchange ◽  
Regulatory Processes ◽  
Predominant Form ◽  
Dependent Protein ◽  
Bona Fide ◽  
Additional Level ◽  
Compact Conformation

Abstract The Ca2+/calmodulin-dependent protein kinase II (CaMKII) assembles into large 12-meric holoenzymes, which is thought to enable regulatory processes required for synaptic plasticity underlying learning, memory and cognition. Here we used single particle electron microscopy (EM) to determine a pseudoatomic model of the CaMKIIα holoenzyme in an extended and activation-competent conformation. The holoenzyme is organized by a rigid central hub complex, while positioning of the kinase domains is highly flexible, revealing dynamic holoenzymes ranging from 15–35 nm in diameter. While most kinase domains are ordered independently, ∼20% appear to form dimers and <3% are consistent with a compact conformation. An additional level of plasticity is revealed by a small fraction of bona-fide 14-mers (<4%) that may enable subunit exchange. Biochemical and cellular FRET studies confirm that the extended state of CaMKIIα resolved by EM is the predominant form of the holoenzyme, even under molecular crowding conditions.

scholarly journals Author response: Molecular mechanism of activation-triggered subunit exchange in Ca2+/calmodulin-dependent protein kinase II

2016 ◽  
Author(s):  
Moitrayee Bhattacharyya ◽  
Margaret M Stratton ◽  
Catherine C Going ◽  
Ethan D McSpadden ◽  
Yongjian Huang ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Molecular Mechanism ◽  
Author Response ◽  
Dependent Protein Kinase ◽  
Subunit Exchange ◽  
Protein Kinase Ii ◽  
Dependent Protein

scholarly journals Molecular mechanism of activation-triggered subunit exchange in Ca2+/calmodulin-dependent protein kinase II

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Moitrayee Bhattacharyya ◽  
Margaret M Stratton ◽  
Catherine C Going ◽  
Ethan D McSpadden ◽  
Yongjian Huang ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Cardiac Function ◽  
Molecular Mechanism ◽  
Kinase Domain ◽  
Dependent Protein Kinase ◽  
Subunit Exchange ◽  
Spiral Form ◽  
Protein Kinase Ii ◽  
Dependent Protein

Activation triggers the exchange of subunits in Ca2+/calmodulin-dependent protein kinase II (CaMKII), an oligomeric enzyme that is critical for learning, memory, and cardiac function. The mechanism by which subunit exchange occurs remains elusive. We show that the human CaMKII holoenzyme exists in dodecameric and tetradecameric forms, and that the calmodulin (CaM)-binding element of CaMKII can bind to the hub of the holoenzyme and destabilize it to release dimers. The structures of CaMKII from two distantly diverged organisms suggest that the CaM-binding element of activated CaMKII acts as a wedge by docking at intersubunit interfaces in the hub. This converts the hub into a spiral form that can release or gain CaMKII dimers. Our data reveal a three-way competition for the CaM-binding element, whereby phosphorylation biases it towards the hub interface, away from the kinase domain and calmodulin, thus unlocking the ability of activated CaMKII holoenzymes to exchange dimers with unactivated ones.

Ca2+, cAMP, and changes in myosin phosphorylation during contraction of smooth muscle

1983 ◽  
Vol 245 (3) ◽  
pp. C255-C270 ◽  
Author(s):  
M. O. Aksoy ◽  
S. Mras ◽  
K. E. Kamm ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Kinase Activity ◽  
Atp Depletion ◽  
Dependent Protein Kinase ◽  
Myosin Phosphorylation ◽  
Cross Bridge ◽  
Regulatory Processes ◽  
Regulatory Systems ◽  
Dependent Protein ◽  
Force Maintenance

Phosphorylation of myosin increases rapidly upon stimulation of an arterial smooth muscle. However, peak values are not maintained and phosphorylation declines, while active stress increases monotonically to a sustained steady state. The aim of this study was to determine the reason(s) for the transient change in myosin phosphorylation. Four hypotheses were considered: 1) reduced substrate, i.e., ATP depletion, 2) altered access of either the myosin kinase or phosphatase to the cross bridge, 3) reduced myosin kinase activity secondary to its phosphorylation by adenosine 3',5'-cyclic monophosphate-dependent protein kinase, and 4) reduced myoplasmic [Ca2+] during the contraction. Our results suggest that the most likely explanation is that there are two Ca2+-dependent regulatory processes: 1) myosin phosphorylation and 2) a second, unidentified site allowing stress maintenance with reduced cross-bridge cycling rates. A higher cell Ca2+ concentration appears to be necessary to activate myosin kinase and produce myosin phosphorylation than is needed for force maintenance. We suggest that agonist-induced Ca2+ transients, coupled with the differential Ca2+ sensitivity of the two regulatory systems, may explain the observed transient in myosin phosphorylation during a maintained contraction in smooth muscle.

scholarly journals Contractile proteins in pericytes. II. Immunocytochemical evidence for the presence of two isomyosins in graded concentrations.

1985 ◽  
Vol 100 (5) ◽  
pp. 1387-1395 ◽  
Author(s):  
N C Joyce ◽  
M F Haire ◽  
G E Palade
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase ◽  
Intestinal Mucosa ◽  
Cyclic Gmp ◽  
Contractile Function ◽  
Dependent Protein Kinase ◽  
Cell Biol ◽  
Predominant Form ◽  
Dependent Protein ◽  
Muscle Isoforms

This paper describes the localization of isomyosins in the pericytes of four rat microvascular beds: heart, diaphragm, pancreas, and the intestinal mucosa, by use of immunoperoxidase techniques and IgGs specific for either nonmuscle or smooth muscle isoforms. Based on the semiquantitative nature of the peroxidatic reaction, we concluded that the amount and distribution of these isoforms vary with the microvascular bed and also with vascular segments within the same bed. In the pericytes of small capillaries, nonmuscle isomyosin is the predominant form, whereas the smooth muscle isomyosin is present in very low concentration. A reversed relationship is found in the pericytes associated with larger capillaries and postcapillary venules. These results, taken together with previous findings on actin (Herman, I., and P. A. D'Amore, 1983, J. Cell Biol. 97:278a), tropomyosin (Joyce, N. C., M. F. Haire, and G. E. Palade, 1985, J. Cell Biol. 100:1379-1386), and cyclic GMP-dependent protein kinase (Joyce, N., P. DeCamilli, and J. Boyles, 1984, Microvasc. Res. 28:206-219), indicate that pericytes contain proteins essential for contraction in higher concentration than any other cells associated with the microvasculature, except smooth muscle cells. Pericytes appear to be, therefore, cells differentiated for a contractile function within the microvasculature.

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