New insights into the functional significance of the acidic region of the unique N-terminal extension of cardiac troponin I

作者：Henze Marcus; Patrick Stacey E; Hinken Aaron; Scruggs Sarah B; Goldspink Paul; de Tombe Pieter P; Kobayashi Minae; Ping Peipei; Kobayashi Tomoyoshi; Solaro R John^*

来源：Biochimica et Biophysica Acta-Molecular Cell Research, 2013, 1833(4): 823-832.

DOI：10.1016/j.bbamcr.2012.08.012

• Cardiac
• Ca-activation
• Phosphorylation
• Cardiomyopathy
• Thin filament

Previous structural studies indicated a special functional role for an acidic region composed of residues 1-10 in the unique N-terminal peptide of cardiac troponin I (cTnI). Employing LC-MS/MS, we determined the presence of phosphorylation sites at S5/S6 in cTnI from wild type mouse hearts as well as in hearts of mice chronically expressing active protein kinase C-epsilon (PKC epsilon) and exhibiting severe dilated cardiomyopathy (DCM). To determine the functional significance of these phosphorylations, we cloned and expressed wild-type cTnI, (Wt), and cTnI variants expressing pseudo-phosphorylation cTnI-(S5D), cTnI(S6D), as well as cTnI(S5A) and cTnI(S6A). We exchanged native Tn of detergent-extracted (skinned) fiber bundles with Tn reconstituted with the variant cTnIs and measured tension and cross-bridge dynamics. Compared to controls, myofilaments controlled by cTnI with pseudo-phosphorylation (S6D) or Ala substitution (S6A) demonstrated a significant depression in maximum tension, ATPase rate, and k(tr), but no change in half-maximally activating Ca2+. In contrast, pseudo-phosphorylation at position 5 (S5D) had no effects, although S5A induced an increase in Ca2+-sensitivity with no change in maximum tension or k(tr). We further tested the impact of acidic domain modifications on myofilament function in studies examining the effects of cTnI(A2V), a mutation linked to DCM. This mutation significantly altered the inhibitory activity of cTnI as well as cooperativity of activation of myofilament tension, but not when S23/S24 were pseudo-phosphorylated. Our data indicate a new functional and pathological role of amino acid modifications in the N-terminal acidic domain of cTnI that is modified by phosphorylations at cTnI(S23/S24). This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

• 出版日期2013-4