Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Based on two criteria, the tightness of packing of myosin rods within the backbone of the filament and the degree of order of the myosin heads, thick filaments isolated from a control group of rat hearts had three different structures. Two of the structures of thick filaments had ordered myosin heads and were distinguishable from each other by the difference in tightness of packing of the myosin rods. Depending on the packing, their structure has been called loose or tight. The third structure had narrow shafts and disordered myosin heads extending at different angles from the backbone. This structure has been called disordered. After phosphorylation of myosin-binding protein C (MyBP-C) with protein kinase A (PKA), almost all thick filaments exhibited the loose structure. Transitions from one structure to another in quiescent muscles were produced by changing the concentration of extracellular Ca. The probability of interaction between isolated thick and thin filaments in control, PKA-treated preparations, and preparations exposed to different Ca concentrations was estimated by electron microscopy. Interactions were more frequent with phosphorylated thick filaments having the loose structure than with either the tight or disordered structure. In view of the presence of MgATP and the absence of Ca, the interaction between the myosin heads and the thin filaments was most likely the weak attachment that precedes the force-generating steps in the cross-bridge cycle. These results suggest that phosphorylation of MyBP-C in cardiac thick filaments increases the probability of cross-bridges forming weak attachments to thin filaments in the absence of activation. This mechanism may modulate the number of cross-bridges generating force during activation.
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PMID:Multiple structures of thick filaments in resting cardiac muscle and their influence on cross-bridge interactions. 1146 48

Ca ions can influence the contraction of cardiac muscle by activating kinases that specifically phosphorylate the myofibrillar proteins myosin-binding protein C (MyBP-C) and the regulatory light chain of myosin (RLC). To investigate the possible role of Ca-regulated phosphorylation of MyBP-C on contraction, isolated quiescent and rhythmically contracting cardiac trabeculae were exposed to different concentrations of extracellular Ca and then chemically skinned to clamp the contractile system. Maximum Ca-activated force (F(max)) was measured in quiescent cells soaking in 1) 2.5 mM Ca for 120 min, 2) 1.25 mM for 120 min, or 3) 1.25 mM for 120 min followed by 10 min in 7.5 mM, and 4) cells rhythmically contracting in 2.5 mM for 20 min. F(max) was, respectively, 21.5, 10.5, 24.7, and 32.6 mN/mm(2). Changes in F(max) were closely associated with changes in the degree of phosphorylation of MyBP-C and occurred at intracellular concentrations of Ca below levels associated with phosphorylation of RLC. Monophosphorylation of MyBP-C by a Ca-regulated kinase is necessary before beta-adrenergic stimulation can produce additional phosphorylation. These results suggest that Ca-dependent phosphorylation of MyBP-C modulates contractility by changing thick filament structure.
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PMID:Changes in cardiac contractility related to calcium-mediated changes in phosphorylation of myosin-binding protein C. 1146 49

Tropomyosin, an essential component of the sarcomere, regulates muscle contraction through Ca(2+)-mediated activation. Familial hypertrophic cardiomyopathy (FHC) is caused by mutations in numerous cardiac sarcomeric proteins, including myosin heavy and light chains, actin, troponin T and I, myosin binding protein C, and alpha-tropomyosin. This study developed transgenic mouse lines that encode an FHC mutation in alpha-tropomyosin; this mutation is an amino acid substitution at codon 180 (Glu180Gly) which occurs in a troponin T binding region. Non-transgenic and control mice expressing wild-type alpha-tropomyosin demonstrate no morphological or physiological changes. Expression of exogenous mutant tropomyosin leads to a concomitant decrease in endogenous alpha-tropomyosin without altering the expression of other contractile proteins. Histological analysis shows that initial pathological changes, which include ventricular concentric hypertrophy, fibrosis and atrial enlargement, are detected within 1 month. The disease-associated changes progressively increase and result in death between 4 and 5 months. Physiological analyses of the FHC mice using echocardiography, work-performing heart analyses, and force measurements of cardiac myofibers, demonstrate dramatic functional differences in diastolic performance and increased sensitivity to calcium. This report demonstrates that mutations in alpha-tropomyosin can be severely disruptive of sarcomeric function, which consequently triggers a dramatic hypertrophic response that culminates in lethality.
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PMID:A familial hypertrophic cardiomyopathy alpha-tropomyosin mutation causes severe cardiac hypertrophy and death in mice. 1160 24

Impaired left ventricular (LV) contractility is a major cause of cardiovascular death, especially congestive heart failure. The identification of susceptibility genes that contribute to impaired LV contractility may uncover mechanisms underlying LV contractile impairment and the development of congestive heart failure. The Hypertension Genetic Epidemiology Network (HyperGEN) collected echocardiographic measurements of myocardial contractility in a large biethnic sample of hypertensive siblings (390 blacks and 398 whites in 179 and 165 sibships, respectively). All participants expressed hypertension before age 60 years, and the mean age of siblings was 52 years in blacks and 61 years in whites. We adjusted myocardial contractility for gender, age, and age(2), and we calculated standardized residuals separately for men and women in both ethnic groups. We conducted multipoint variance components linkage analysis using GENEHUNTER2 and 387 anonymous markers (CHCL8 marker set). We found evidence for significant linkage to a microsatellite marker, D11S1993 (lod, 3.93 in blacks), approximately 54 cM from the tip of the short arm of chromosome 11, that accounted for 72% of the phenotypic variation in LV contractility. A chromosome 22 locus showed suggestive evidence for linkage (lod, 2.83 in whites and 1.15 in blacks). The chromosome 11 peak coincides with the region containing myosin-binding protein C. Mutations in this gene are linked to familial hypertrophic cardiomyopathy. Our results show strong evidence for linkage of a region of chromosome 11 with LV contractility in blacks and suggest that an important gene for impaired LV contractility is harbored in this region.
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PMID:Linkage of left ventricular contractility to chromosome 11 in humans: The HyperGEN Study. 1164 Dec 84

beta-Adrenergic stimulation increases stroke volume in mammalian hearts as a result of protein kinase A (PKA)-induced phosphorylation of several myocyte proteins. This study investigated whether PKA-induced phosphorylation of myofibrillar proteins directly affects myocyte contractility. To test this possibility, we compared isometric force, loaded shortening velocity, and power output in skinned rat cardiac myocytes before and after treatment with the catalytic subunit of PKA. Consistent with previous studies, PKA increased phosphorylation levels of myosin binding protein C and troponin I, and reduced Ca(2+) sensitivity of force. PKA also significantly increased both maximal force (25.4+/-8.3 versus 31.6+/-11.3 microN [P<0.001, n=12]) and peak absolute power output (2.48+/-1.33 versus 3.38+/-1.52 microW/mg [P<0.05, n=5]) during maximal Ca(2+) activations. Furthermore, PKA elevated power output at nearly all loads even after normalizing for the increase in force. After PKA treatment, peak normalized power output increased approximately 20% during maximal Ca(2+) activations (n=5) and approximately 33% during half-maximal Ca(2+) activations (n=9). These results indicate that PKA-induced phosphorylation of myofibrillar proteins increases the power output-generating capacity of skinned cardiac myocytes, in part, by speeding the step(s) in the crossbridge cycle that limit loaded shortening rates, and these changes likely contribute to greater contractility in hearts after beta-adrenergic stimulation.
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PMID:Power output is increased after phosphorylation of myofibrillar proteins in rat skinned cardiac myocytes. 1173 84

Inotropic agents that increase the intracellular levels of cAMP have been shown to increase crossbridge turnover kinetics in intact rat ventricular muscle, as measured by the parameter f(min) (the frequency at which dynamic stiffness is minimum). These agents are also known to increase the level of phosphorylation of two candidate myofibrillar proteins: myosin binding protein C (MyBPC) and Troponin I (TnI), but have no effect on myosin light chain 2 phosphorylation (MyLC2). The aim of this study was to investigate whether the phosphorylation of TnI and/or MyBPC was responsible for the increase in crossbridge cycling kinetics (as captured by f(min)) seen with the elevation of cAMP within cardiac tissue. Using barium-activated intact rat papillary muscle, we investigated the actions of isobutylmethylxanthine (IBMX), an inhibitor of cAMP-dependent phosphatase, which simulates the action of beta-adrenergic agents, and the chemical phosphatase 2,3-butanedione monoxime (BDM), which has been shown to dephosphorylate a number of contractile proteins. The presence of 0.6 mM IBMX approximately doubled the f(min) value of intact rat papillary muscle. This action was unaffected by the addition of BDM. In the presence of IBMX and BDM, the level of phosphorylation of MyBPC was unchanged, that of MyLC2 was reduced to 60 % of control, yet that of TnI was markedly increased (to 30 % above control levels). We conclude that TnI phosphorylation, mediated by cAMP-dependent protein kinase A, is the molecular basis for the enhanced crossbridge cycling seen during beta-adrenergic stimulation of the heart.
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PMID:Troponin I phosphorylation enhances crossbridge kinetics during beta-adrenergic stimulation in rat cardiac tissue. 1215 88

Mutations in sarcomeric protein genes have been reported to cause dilated cardiomyopathy (DCM). In order to detect novel mutations we screened the sarcomeric protein genes beta-myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), troponin T (TNNT2), and alpha-tropomyosin (TPM1) in 46 young patients with DCM. Mutation screening was done using single-strand conformation polymorphism (SSCP) analysis and DNA sequencing. The mutations in MYH7 were projected onto the protein data bank-structure (pdb) of myosin of striated muscle. In MYH7 two mutations (Ala223Thr and Ser642Leu) were found in two patients. Ser642Leu is part of the actin-myosin interface. Ala223Thr affects a buried residue near the ATP binding site. In MYBPC3 we found one missense mutation (Asn948Thr) in a male patient. None of the mutations were found in 88 healthy controls and in 136 patients with hypertrophic cardiomyopathy (HCM). Thus mutations in HCM causing genes are not rare in DCM and have potential for functional relevance.
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PMID:Novel mutations in sarcomeric protein genes in dilated cardiomyopathy. 1237 28

Cyclic AMP-dependent protein kinase (PKA) targets contractile proteins, troponin-I (TnI) and myosin binding protein C (MyBP-C) in the heart and induces a decrease in myofilament Ca2+ sensitivity. Yet, the effect of sarcomere length (SL) change on Ca2+ sensitivity (length-dependent activation: LDA) following PKA-dependent phosphorylation is not clear. To clarify the role of PKA-dependent phosphorylation of TnI and MyBP-C on LDA in the heart, we examined LDA in skinned myocytes from a non-transgenic (NTG) and a transgenic murine model in which the native cardiac isoform (cTnI) was completely replaced by the slow skeletal isoform of TnI (ssTnI-TG) lacking the phosphorylation sites for PKA, while retaining PKA sites on MyBP-C. In NTG myocytes, PKA treatment decreased Ca2+ sensitivity at each SL, but enhanced the impact of SL change on Ca2+ sensitivity. Despite a greater sensitivity to Ca2+ and a reduction in LDA, neither Ca2+ responsiveness nor LDA was affected by PKA treatment in ssTnI-TG myocytes. To determine whether the above observations could be explained by the lateral separation between thick and thin filaments, as suggested by others, we measured interfilament spacing by X-ray diffraction as a function of SL in skinned cardiac trabeculae in the passive state from both NTG and ssTnI-TG models before and following treatment with PKA. Phosphorylation by PKA increased lattice spacing at every SL in NTG trabeculae. However, the relationship between SL and myofilament lattice spacing in ssTnI-TG was markedly shifted downward to an overall decreased myofilament lattice spacing following PKA treatment. We conclude: (1) PKA-dependent phosphorylation enhances length-dependent activation in NTG hearts; (2) replacement of native TnI with ssTnI increases Ca2+ sensitivity of tension but reduces length-dependent activation; (3) MyBP-C phosphorylation by PKA does not alter calcium responsiveness and induces a decrease in myofilament lattice spacing at all sarcomere lengths and (4) length-dependent activation in the heart cannot be entirely explained by alterations in myofilament lattice spacing.
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PMID:Troponin I in the murine myocardium: influence on length-dependent activation and interfilament spacing. 1256 15

Spindle alignment is the process in which the two spindle poles are directed toward preselected and opposite cell ends. In budding yeast, the APC-related molecule Kar9 is required for proper alignment of the spindle with the mother-bud axis. We find that Kar9 localizes to the prospective daughter cell spindle pole. Kar9 is transferred from the pole to cytoplasmic microtubules, which are then guided in a myosin-dependent manner to the bud. Clb4/Cdc28 kinase phosphorylates Kar9 and accumulates on the pole destined to the mother cell. Mutations that block phosphorylation at Cdc28 consensus sites result in localization of Kar9 to both poles and target them both to the bud. Thus, Clb4/Cdc28 prevents Kar9 loading on the mother bound pole. In turn, asymmetric distribution of Kar9 ensures that only one pole orients toward the bud. Our results indicate that Cdk1-dependent spindle asymmetry ensures proper alignment of the mitotic spindle with the cell division axis.
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PMID:Asymmetric loading of Kar9 onto spindle poles and microtubules ensures proper spindle alignment. 1263 9

Striated craniofacial and limb muscles differ in their embryological origin, regulatory program during myogenesis, and innervation. In an attempt to explore the effects of these differences on the striated muscle phenotype in humans, the expression of myosin and myosin-associated thick filament proteins were studied at the single fiber level both in the human jaw-closing masseter muscle and in two limb muscles (biceps brachii and quadriceps femoris muscles). In the masseter, unique combinations of myosin heavy chain (MyHC) and myosin binding protein C (MyBP-C) isoforms were observed at the single fiber level. Compared to the limb muscles, the MyHC isoform expression was more complex in the masseter while the opposite was observed for MyBP-C. In limb muscles, a coordinated expression of three MyHC and three MyBP-C isoforms were observed, i.e., single fibers contained one or two MyHC isoforms, and up to three MyBP-C isoforms. Also, the relative content of the different MyBP-C isoforms correlated with the MyHC isoform expression. In the masseter, on the other hand, up to five different MyHC isoforms could be observed in the same fiber, but only one MyBP-C isoform was identified irrespective MyHC isoform expression. This MyBP-C isoform had a migration rate similar to the slow MyBP-C isoform in limb muscle fibers. In conclusion, a unique myofibrillar protein isoform expression was observed in the human masseter muscle fibers, suggesting significant differences in structural and functional properties between muscle fibers from human masseter and limb muscles.
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PMID:Human single masseter muscle fibers contain unique combinations of myosin and myosin binding protein C isoforms. 1263 Jul 6


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