Cardiac myosin regulatory light chain kinase modulates cardiac contractility by phosphorylating both myosin regulatory light chain and troponin I.
Heart muscle contractility and performance are controlled by posttranslational modifications of sarcomeric proteins. Although myosin regulatory light chain (RLC) phosphorylation has been studied extensively in vitro and in vivo, the precise role of cardiac myosin light chain kinase (cMLCK), the primary kinase acting upon RLC, in the regulation of cardiomyocyte contractility remains poorly understood. In this study, using recombinantly expressed and purified proteins, various analytical methods, in vitro and in situ kinase assays, and mechanical measurements in isolated ventricular trabeculae, we demonstrate that human cMLCK is not a dedicated kinase for RLC but can phosphorylate other sarcomeric proteins with well-characterized regulatory functions. We show that cMLCK specifically monophosphorylates Ser23 of human cardiac troponin I (cTnI) in isolation and in the trimeric troponin complex in vitro and in situ in the native environment of the muscle myofilament lattice. Moreover, we observed that human cMLCK phosphorylates rodent cTnI to a much smaller extent in vitro and in situ, suggesting species-specific adaptation of cMLCK. Although cMLCK treatment of ventricular trabeculae exchanged with rat or human troponin increased their cross-bridge kinetics, the increase in sensitivity of myofilaments to calcium was significantly blunted by human TnI, suggesting that human cTnI phosphorylation by cMLCK modifies the functional consequences of RLC phosphorylation. We propose that cMLCK-mediated phosphorylation of TnI is functionally significant and represents a critical signaling pathway that coordinates the regulatory states of thick and thin filaments in both physiological and potentially pathophysiological conditions of the heart.
['Sevrieva|Ivanka R|IR|0000-0001-8471-6484', 'Brandmeier|Birgit|B|', 'Ponnam|Saraswathi|S|', 'Gautel|Mathias|M|', 'Irving|Malcolm|M|', 'Campbell|Kenneth S|KS|', 'Sun|Yin-Biao|YB|0000-0002-4992-8198', 'Kampourakis|Thomas|T|']
D000818:Animals D002118:Calcium D006801:Humans D008297:Male D009200:Myocardial Contraction D009206:Myocardium D009210:Myofibrils D018994:Myosin Light Chains D009219:Myosin-Light-Chain Kinase D010455:Peptides D010766:Phosphorylation D051381:Rats D017208:Rats, Wistar D011994:Recombinant Proteins D015398:Signal Transduction D019210:Troponin I
myosin troponin cardiac myosin light chain kinase cardiomyocyte calcium signalling cardiac muscle regulation contractile protein heart function posttranslational modification (PTM) troponin I phosphorylation