{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,27]],"date-time":"2026-10-27T20:46:48Z","timestamp":1793134008855,"version":"4.5.0"},"reference-count":37,"publisher":"Ovid Technologies (Wolters Kluwer Health)","issue":"1","content-domain":{"domain":["www.ahajournals.org"],"crossmark-restriction":true},"short-container-title":["Circulation Research"],"published-print":{"date-parts":[[2009,1,2]]},"abstract":"<jats:p>The sarcomeric titin springs influence myocardial distensibility and passive stiffness. Titin isoform composition and protein kinase (PK)A-dependent titin phosphorylation are variables contributing to diastolic heart function. However, diastolic tone, relaxation speed, and left ventricular extensibility are also altered by PKG activation. We used back-phosphorylation assays to determine whether PKG can phosphorylate titin and affect titin-based stiffness in skinned myofibers and isolated myofibrils. PKG in the presence of 8-pCPT-cGMP (cGMP) phosphorylated the 2 main cardiac titin isoforms, N2BA and N2B, in human and canine left ventricles. In human myofibers\/myofibrils dephosphorylated before mechanical analysis, passive stiffness dropped 10% to 20% on application of cGMP-PKG. Autoradiography and anti-phosphoserine blotting of recombinant human I-band titin domains established that PKG phosphorylates the N2-B and N2-A domains of titin. Using site-directed mutagenesis, serine residue S469 near the COOH terminus of the cardiac N2-B\u2013unique sequence (N2-Bus) was identified as a PKG and PKA phosphorylation site. To address the mechanism of the PKG effect on titin stiffness, single-molecule atomic force microscopy force\u2013extension experiments were performed on engineered N2-Bus\u2013containing constructs. The presence of cGMP-PKG increased the bending rigidity of the N2-Bus to a degree that explained the overall PKG-mediated decrease in cardiomyofibrillar stiffness. Thus, the mechanically relevant site of PKG-induced titin phosphorylation is most likely in the N2-Bus; phosphorylation of other titin sites could affect protein\u2013protein interactions. The results suggest that reducing titin stiffness by PKG-dependent phosphorylation of the N2-Bus can benefit diastolic function. Failing human hearts revealed a deficit for basal titin phosphorylation compared to donor hearts, which may contribute to diastolic dysfunction in heart failure.<\/jats:p>","DOI":"10.1161\/circresaha.108.184408","type":"journal-article","created":{"date-parts":[[2008,11,20]],"date-time":"2008-11-20T21:50:08Z","timestamp":1227217808000},"page":"87-94","update-policy":"https:\/\/doi.org\/10.1161\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":387,"title":["Protein Kinase G Modulates Human Myocardial Passive Stiffness by Phosphorylation of the Titin Springs"],"prefix":"10.1161","volume":"104","author":[{"given":"Martina","family":"Kru\u0308ger","sequence":"first","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sebastian","family":"Ko\u0308tter","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Anika","family":"Gru\u0308tzner","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Patrick","family":"Lang","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Christian","family":"Andresen","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Margaret M.","family":"Redfield","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elke","family":"Butt","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cris G.","family":"dos Remedios","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wolfgang A.","family":"Linke","sequence":"additional","affiliation":[{"name":"From the Physiology and Biophysics Unit (M.K., S.K., A.G., P.L., C.A., W.A.L.), University of Muenster, Germany; Mayo Foundation (M.M.R.), Rochester, Minn; Institute of Clinical Biochemistry and Pathobiochemistry (E.B.), University of Wurzburg, Germany; and Muscle Research Unit (C.G.d.R.), Bosch Institute, University of Sydney, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"276","reference":[{"key":"e_1_3_3_1_2","doi-asserted-by":"publisher","DOI":"10.1161\/res.86.11.1114"},{"key":"e_1_3_3_2_2","first-page":"637","volume":"77","year":"2008","unstructured":"Linke WA. 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