Purification and characterization of a Ca²⁺/calmodulin‐dependent protein kinase II from hog gastric mucosa using a protein‐protein affinity chromatographic technique

Abstract

A peripheral member of the Ca 2ϩ /calmodulin-dependent protein kinase II (CaMkinase II) group has been purified from hog gastric mucosa with the use of a novel affinity-chromatographic step. For the well known neural isotypes of CaMkinase II, it is proposed that the subunits form holoenzymes through a specific domain at the C-terminus called the 'association domain'. We immobilized a bacterially expressed association domain from CaMkinase II-δ-2 and used it as an affinity column. This matrix was used as the last step in a sequential enzyme purification procedure from hog gastric mucosa and yielded a homogeneous CaMkinase II which showed the typical physical and enzymatic properties of CaMkinase II. The enzyme activity showed a dependence on Ca 2ϩ and calmodulin (apparent K 0.5 ϭ 2.7 µM and K 0.5 ϭ 0.02 µM, respectively). We found a subunit molecular mass of 61 kDa. An apparent native molecular mass of 310 kDa was calculated. The Stokes radius and the sedimentation coefficient were 6.7 nm and 11.2 S, respectively. Moreover, the isolated CaMkinase II was very well inhibited by the CaMkinase-IIspecific inhibitors KN-62 (K i ϭ 0.52 nM) and KT5926 (K i ϭ 0.79 nM). The phosphorylation of several substrates revealed its multifunctionality. The purified CaMkinase II had an apparent K m for Mg-ATP of 24.0 µM and for autocamtide-II of 0.62 µM. CaMkinase II is considered as a strong candidate for regulating vesicle released quanta such as acid, neurotransmitters or insulin.Keywords : calmodulin; Ca 2ϩ /calmodulin-dependent protein kinase II ; protein kinase ; purification; affinity chromatography.In gastric parietal cells, at least three major cellular pathways bachol, histamine and forskolin on acid secretion in isolated rabbit gastric parietal cells with K i values of 0.15, 0.3 and 1 µM, mediate an agonist-induced acid secretion [1, 2]. Stimulation of the histaminic receptor H 2 causes the activation of the cAMP respectively. The main effect seemed to be unspecific on the pH gradient formation level [17]. pathway, followed by an unknown acid-secretion mechanism [3]. Another way of acid secretion is muscarinic M 3 receptorThe Ca 2ϩ /calmodulin-dependent protein kinases II are coded for by four genes. The isoforms are named A, β, γ and δ, all mediated [4Ϫ10], which activates phospholipase C, resulting in cleavage of phosphatidylinositol 4,5-bisphosphate into inositol established first in neural tissues [20Ϫ25]. The best characterized isoforms are mammalian CaMkinase II-A (50Ϫ54 kDa) 1,4,5-trisphosphate and diacylglycerol. Gastrin also elevates the intracellular calcium concentration [11]. A subsequent rise in and -β (58Ϫ60 kDa), which are rarely found in non-neural tissues. Both isotypes form holoenzymes of 10 and 8 subunits, cytosolic Ca 2ϩ activates Ca 2ϩ -dependent processes. A major target for Ca 2ϩ binding is the ubiquitous calmodulin [12Ϫ14]. respectively, which are likely homomeric [26]. The CaMkinase II isoforms γ and δ have only been characterized at the cDNA We recently found γ and δ subunits of Ca 2ϩ /calmodulin...

The Stability of a Stochastic CaMKII Switch: Dependence on the Number of Enzyme Molecules and Protein Turnover

“…First, the initial (P0 to P1) phosphorylation step must be significantly slower than further phosphorylation steps. This is true as the Hill constant for Ca 2+ activation of CaMKII [38,39] is significantly greater than the average Ca 2+ concentration in the physiological resting state (0.7 μM versus 0.1 μM in most of this paper). Second, the phosphatase activity must saturate so the rate of dephosphorylation per phosphorylated subunit is significantly slower in the UP state than in the DOWN state.…”

Cloning and quantitative determination of the human Ca 2+ /calmodulin-dependent protein kinase II (CaMK II) isoforms in human beta cells

“…The precise role of this region is not known but it is thought it enables the protein to associate with subcellular organelles and cytoskeletal structures [19]. The C-terminal part of the enzyme is responsible for oligomerisation of CaMK II allowing for the association of 6 to 12 subunits [1,20]. Cells can contain more than a single isoform of the kinase and both, homomultimers and heteromultimers, of the kinase can exist.…”

Different actions of protein kinase C isoforms α and ε on gastric acid secretion

“…The key signalling protein kinase in cholinergic stimulation of H + secretion is CaMKII (Tsunoda et al ., 1992; Mayer et al ., 1994; Fährmann et al ., 1998; 1999; 2002; Fährmann & Pfeiffer, 1999; 2000). Carbachol‐stimulation causes a doubling of CaMKII activity (Figure 4a), as well as a strong increase of autoactivated CaMKII in the secretory apical membrane of rabbit gastric mucosal cells (Figure 4b).…”

“…The main intracellular regulator of carbachol‐induced H + secretion appears to be CaMKII (Fährmann et al ., 2002). CaMKII is abundant in gastric mucosa as holoenzyme (Fährmann et al ., 1998; Fährmann & Pfeiffer, 2000). Carbachol‐stimulation both induces translocation of CaMKII to the apical membrane of rat mucosal cells as well as a strong activation of CaMKII phosphotransferase activity (Fährmann et al ., 2002).…”