alpha KAP is an anchoring protein for a novel CaM kinase II isoform in skeletal muscle

Abstract

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) is present in a membrane-bound form that phosphorylates synapsin I on neuronal synaptic vesicles and the ryanodine receptor at skeletal muscle sarcoplasmic reticulum (SR), but it is unclear how this soluble enzyme is targeted to membranes. We demonstrate that alphaKAP, a non-kinase protein encoded by a gene within the gene of alpha-CaM kinase II, can target the CaM kinase II holoenzyme to the SR membrane. Our results indicate that alphaKAP (i) is anchored to the membrane via its N-terminal hydrophobic domain, (ii) can co-assemble with catalytically competent CaM kinase II isoforms and target them to the membrane regardless of their state of activation, and (iii) is co-localized and associated with rat skeletal muscle CaM kinase II in vivo. alphaKAP is therefore the first demonstrated anchoring protein for CaM kinase II. CaM kinase II assembled with alphaKAP retains normal enzymatic activity and the ability to become Ca2+-independent following autophosphorylation. A new variant of beta-CaM kinase II, termed betaM-CaM kinase II, is one of the predominant CaM kinase II isoforms associated with alphaKAP in skeletal muscle SR.

α-Kinase Anchoring Protein αKAP Interacts with SERCA2A to Spatially Position Ca2+/Calmodulin-dependent Protein Kinase II and Modulate Phospholamban Phosphorylation

“…Data also suggest that ␣KAP along with the novel CaMKII␤ 4 are enriched in cardiac SR membranes implying a common regulatory role for these molecules in these two muscle types (13)(14)(15). Further, studies suggest a significant level of a muscle-specific CaMKII ␤ isoform (CaMKII␤ 4 ) in cardiac and skeletal muscle (14 -16).…”

“…Although four different isoforms of CaMKII (␣, ␤, ␦, and ␥) are expressed in a tissuespecific manner, cardiac tissue is shown to have predominance of CaMKII␦ C (cytosolic) and CaMKII␦ B (nuclear) isoforms, which serve roles in excitation-contraction coupling and cell growth, respectively (7, 12). Studies have also revealed a significant level of a muscle-specific CaMKII ␤ isoform (CaMKII␤ 4 ) in skeletal and cardiac muscle (11,(13)(14)(15). In addition, the CAMK2A gene that encodes CaMKII␣ kinase in brain expresses an alternatively spliced non-kinase polypeptide designated ␣KAP in cardiac and skeletal muscle (14 -16).…”

“…The ␣KAP has a unique amino acid stretch at the N terminus, which encodes a putative transmembrane domain, followed by the association domain of CaMKII␣. The association domain in the CaMKII gene family is a common feature important for oligomerization (15)(16)(17).␣KAP is believed to be targeted to the SR membrane in skeletal muscle via the N-terminal hydrophobic sequence and has been proposed to recruit the muscle-specific CaMKII␤ 4 through dimerization with the association domain and regulate calcium transport (15). Data also suggest that ␣KAP along with the novel CaMKII␤ 4 are enriched in cardiac SR membranes implying a common regulatory role for these molecules in these two muscle types (13-15).…”

“…The ␣KAP has a unique amino acid stretch at the N terminus, which encodes a putative transmembrane domain, followed by the association domain of CaMKII␣. The association domain in the CaMKII gene family is a common feature important for oligomerization (15)(16)(17) …”

Chronic Antidepressants Induce Redistribution and Differential Activation of αCaM Kinase II between Presynaptic Compartments

“…CaM kinase II is a multifunctional and ubiquitous enzyme and it was shown recently that targeting of the kinase to distinct subcellular compartments is crucial to its specificity of action in terms of space and time (Griffith et al, 2003). Targeting of the kinase to the nucleus, cytoskeleton, sarcoplasmic reticulum, and postsynaptic density of dendritic spines is achieved by several mechanisms, including alternative splicing of sequences containing nuclear localization signal, change of a/b isoform ratio, alternatively splicing-generated anchoring protein (aCaM kinase II association protein, aKAP), activity-dependent-regulated dendritic translation, and binding to N-methyl-D-aspartate (NMDA) receptors (Srinivasan et al, 1994;Bayer et al, 1998;Ouyang et al, 1999;Shen et al, 1998Shen et al, , 2000Fink et al, 2003).…”