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Marion L Greaser

Publications and source records attributed to Marion L Greaser.

10 recordsLinked to original sources
PubMed2006

Studies on titin PEVK peptides and their interaction.

Experiments were conducted on several synthetic and expressed peptides from the PEVK region of titin, the giant muscle protein. Different secondary structure prediction methods based on amino acid sequence gave estimates ranging from over 70% alpha helical to no helix (totally disordered) for the polyE peptide corresponding to human exon 115. Circular dichroism (CD) experiments demonstrated that both the positively charged PPAK modules and the negatively charged PolyE repeats had similar spectral properties with disordered secondary structure predominating. Gel permeation chromatography showed that both PPAK and polyE peptides had 2-4 times larger Stokes radii than expected from their molecular mass. Mixtures of the oppositely charged titin peptides caused no change in apparent secondary structure as observed by circular dichroism or migration properties using native gel electrophoresis. Similarly addition of calcium did not alter the CD spectra or peptide electrophoretic mobility of the individual peptides or their mixtures. The properties of both the PPAK and polyE type peptides suggest that both had most of the characteristic properties to be classified as intrinsically disordered proteins.

Amino Acid Sequence↗
PubMed2005

Muscle LIM protein plays both structural and functional roles in skeletal muscle.

Muscle LIM protein (MLP) has been suggested to be an important mediator of mechanical stress in cardiac tissue, but the role that it plays in skeletal muscle remains unclear. Previous studies have shown that it is dramatically upregulated in fast-to-slow fiber-type transformation and also after eccentric contraction (EC)-induced muscle injury. The functional consequences of this upregulation, if any, are unclear. In the present study, we have examined the skeletal muscle phenotype of MLP-knockout (MLPKO) mice in terms of their response to EC-induced muscle injuries. The data suggest that while the MLPKO mice recover completely after EC-induced injury, their torque production lags behind that of heterozygous littermates in the early stages of the recovery process. This lag is accompanied by decreased expression of the muscle regulatory factor MyoD, suggesting that MLP may influence gene expression. In addition, there is evidence of type I fiber atrophy and a shorter resting sarcomere length in the MLPKO mice, but no significant differences in fiber type distribution. In summary, MLP appears to play a subtle role in the maintenance of normal muscle characteristics and in the early events of the recovery process of skeletal muscle to injury, serving both structural and gene-regulatory roles.

Animals↗
PubMed2005

Developmental changes in rat cardiac titin/connectin: transitions in normal animals and in mutants with a delayed pattern of isoform transition.

Rat cardiac titin undergoes developmental changes in isoform expression during the period from late embryonic through the first 20-25 days of life. At least five size classes of titin isoforms have been identified using SDS agarose gel electrophoresis. The longest normal isoform is expressed in the embryonic stages, and it is progressively replaced with increasingly smaller versions. The isoform switching is consistent with changes in resting tension from lower values in one-day neonates to higher levels in adult myocytes. Considerable micro-heterogeneity in alternative splicing patterns also was found, particularly in the N2BA PEVK region of human, rat, and dog ventricle. A rat mutation has been identified in which the embryonic-neonatal titin isoform transitions are markedly delayed. These mutant animals may prove useful for examining the role of titin in stretch-activated signal transduction and in the Frank-Starling relationship.

Alternative Splicing↗
PubMed2004

Titin isoform changes in rat myocardium during development.

Developmental changes in the alternative splicing patterns of titin were observed in rat cardiac muscle. Titin from 16-day fetal hearts consisted of a single 3710 kDa band on SDS agarose gels, and it disappeared by 10 days after birth. The major adult N2B isoform (2990 kDa) first appeared in 18-day fetal hearts and its proportion in the ventricle increased to approximately 85% from 20 days of age and older. Changes in three other intermediate-sized N2BA isoform bands also occurred during this same time period. The cDNA sequences of fetal cardiac, adult ventricle, and adult soleus were different in the PEVK and alternatively spliced middle Ig domain. Extensive heterogeneity in splice patterns was found in the N2BA PEVK region. The extra length of the fetal titin isoforms appeared to be due to both a greater number of middle Ig domains expressed plus the inclusion of more PEVK exons. Passive tension measurements on myocyte-sized fragments indicated a significantly lower tension in neonate versus adult ventricles at sarcomere lengths greater than 2.1 microm, consistent with the protein and cDNA sequence results. The time course of the titin isoform switching was similar to that occurring with myosin and troponin I during development.

Alternative Splicing↗
PubMed2003

Titin isoform expression in normal and hypertensive myocardium.

OBJECTIVE: Titin isoform expression patterns were examined to explain previously observed genetic differences in rat cardiac passive tension. METHODS: Rat ventricles from male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats (normotensive) were used to analyze the titin isoform patterns. The hypertensive status was verified by blood pressure measurements and heart weight to body weight ratios. Gel electrophoresis and scanning densitometry were performed to determine ratios of myosin heavy chain and titin isoforms expressed. In situ hybridization using a cRNA probe specific for N2BA titin and a positive control in the N2B unique region was used to demonstrate tissue location of the titin message. RESULTS: Regression analysis of titin isoform ratios, myosin heavy chain isoform ratios, and heart weight to body weight ratios all suggest a smaller proportion of N2BA titin (longer isoform) was expressed in rat left ventricles with increased hypertrophy. In situ hybridization showed that the N2BA and N2B isoforms were co-expressed within most of the cardiomyocytes. Agarose gel electrophoresis demonstrated two different N2BA titin isoforms in all rat ventricles. CONCLUSIONS: Expression of less N2BA and more N2B titin in response to pressure overload will result in higher passive tension upon stretch at a given sarcomere length and thus affect cardiac performance.

Animals↗
PubMed2003

Vertical agarose gel electrophoresis and electroblotting of high-molecular-weight proteins.

The electrophoretic separation of high-molecular-weight proteins (> 500 kDa) using polyacrylamide is difficult because gels with a large enough pore size for adequate protein mobility are mechanically unstable. A 1% vertical sodium dodecyl sulfate (SDS)-agarose gel electrophoresis (VAGE) system has been developed that allows titin (a protein with the largest known SDS subunit size of 3000-4000 kDa) to migrate over 10 cm in a approximately 13 cm resolving gel. Such migration gives clear and reproducible separation of titin isoforms. Proteins ranging in size from myosin heavy chain ( approximately 220 kDa) up to titin can be resolved on this gel system. Electroblotting of these very large proteins was nearly 100% efficient. This VAGE system has revealed two titin size variants in rabbit psoas muscle, two N2BA bands in rabbit cardiac muscle, and species differences between titins from rat and rabbit muscle. Agarose electrophoresis should be the method of choice for separation and blotting of proteins with very large subunit sizes.

Animals↗
PubMed2002

Solution structure of heavy meromyosin by small-angle scattering.

Elucidation of x-ray crystal structures for the S1 subfragment of myosin afforded atomic resolution of the nucleotide and actin binding sites of the enzyme. The structures have led to more detailed hypotheses regarding the mechanisms by which force generation is coupled to ATP hydrolysis. However, the three-dimensional structure of double-headed myosin consisting of two S1 subfragments has not yet been solved. Therefore, to investigate the overall shape and relative orientations of the two heads of myosin, we performed small-angle x-ray and neutron scattering measurements of heavy meromyosin containing all three light chains (LC(1-3)) in solution. The resulting small-angle scattering intensity profiles were best fit by models of the heavy meromyosin head-tail junction in which the angular separation between heads was less than 180 degrees. The S1 heads of the best fit models are not related by an axis of symmetry, and one of the two S1 heads is bent back along the rod. These results provide new information on the structure of the head-tail junction of myosin and indicate that combining scattering measurements with high resolution structural modeling is a feasible approach for investigating myosin head-head interactions in solution.

Animals↗
PubMed2002

Hypertrophic cardiomyopathy in cardiac myosin binding protein-C knockout mice.

Familial hypertrophic cardiomyopathy (FHC) is an inherited autosomal dominant disease caused by mutations in sarcomeric proteins. Among these, mutations that affect myosin binding protein-C (MyBP-C), an abundant component of the thick filaments, account for 20% to 30% of all mutations linked to FHC. However, the mechanisms by which MyBP-C mutations cause disease and the function of MyBP-C are not well understood. Therefore, to assess deficits due to elimination of MyBP-C, we used gene targeting to produce a knockout mouse that lacks MyBP-C in the heart. Knockout mice were produced by deletion of exons 3 to 10 from the endogenous cardiac (c) MyBP-C gene in murine embryonic stem (ES) cells and subsequent breeding of chimeric founder mice to obtain mice heterozygous (+/-) and homozygous (-/-) for the knockout allele. Wild-type (+/+), cMyBP-C(+/-), and cMyBP-C(-/-) mice were born in accordance with Mendelian inheritance ratios, survived into adulthood, and were fertile. Western blot analyses confirmed that cMyBP-C was absent in hearts of homozygous knockout mice. Whereas cMyBP-C(+/-) mice were indistinguishable from wild-type littermates, cMyBP-C(-/-) mice exhibited significant cardiac hypertrophy. Cardiac function, assessed using 2-dimensionally guided M-mode echocardiography, showed significantly depressed indices of diastolic and systolic function only in cMyBP-C(-/-) mice. Ca2+ sensitivity of tension, measured in single skinned myocytes, was reduced in cMyBP-C(-/-) but not cMyBP-C(+/-) mice. These results establish that cMyBP-C is not essential for cardiac development but that the absence of cMyBP-C results in profound cardiac hypertrophy and impaired contractile function.

Actin Cytoskeleton↗
PubMed2002

Species variations in cDNA sequence and exon splicing patterns in the extensible I-band region of cardiac titin: relation to passive tension.

Titin is believed to play a major role in passive tension development in cardiac muscle. The cDNA sequence of cardiac titin in the I-band sarcomeric region was determined for several mammalian species. Contiguous sequences of 3749, 12,230, 6602, and 11,850 base pairs have been obtained for the rat N2B, rat N2BA, dog N2B, and dog N2BA isoforms respectively. The length of the PEVK region of the N2B isoform did not correlate with rest tension properties since the only species showing an altered length was the dog that expressed a shorter form. No differences were found between the N2B PEVK lengths in ventricular and atrial muscle. New N2BA splicing pathways in the first tandem Ig region were found in human and dog cardiac muscle. Most of the rat and dog sequences were 85-95% identical with the reported human sequence. However, the N2B unique amino acid sequences of rat and dog were only 51 and 67% identical to human. The rat N2B unique sequence was 526 amino acids in length compared to 572 in human. The difference in length was due to deletion of amino acid segments from six different regions of the N2B unique domain. Patterns of PEVK exon expression were also much different in the dog, human, and rat. Six separate dog N2BA PEVK clones were sequenced, and all had different exon splice combinations yielding PEVK lengths ranging from 703 to 900 amino acids. In contrast a rat N2BA clone had a PEVK length of 525 amino acids, while a human clone had an 908 amino acid PEVK segment. Thus, in addition to the higher proportion of the shorter N2B isoform found in rat compared with dog cardiac muscle observed previously, shorter N2B unique and N2BA PEVK segments may also contribute to the greater passive tension in cardiac muscle from rats.

Amino Acid Sequence↗