Niederhoffer Muscle Biochemistry C2000

Muscle Biochemistry

Eric C. Niederhoffer, Ph.D.

Associate Professor, Biochemistry & Molecular Biology

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Overview
Resources (Where to go for more)
Muscle organization (What it looks like)
Muscle proteins (Who's involved)
Metabolic pathways (What powers muscle)
Role of calcium (What a small signal)
Resources
Neuromuscular Home Page (Washington University)
Muscle contraction (animated GIF, QuickTime1, QuickTime2)
Brown, R. H., Jr. 1997. Dystrophin-associated proteins and the muscular dystrophies. Annual Review of Medicine 48:457-466.
Carlson, C. G. 1998. The dystrophinopathies: an alternative to the structural hypothesis. Neurobiology of Disease 5:3-15.
Devlin, T. M. (ed.). 1997. Textbook of biochemistry with clinical correlations, 4th ed. John Wiley & Sons, Inc., New York.
Geeves, M.A., and K. C. Holmes. 1999. Structural mechanism of muscle contraction. Annual Review of Biochemistry 68:687-728.
Mendell, J.R., R. C. Griggs, and L. J. Ptácek. 1998. Diseases of muscle, pp. 2473-2483. In A. S. Fauci, E. Braunwald, K. J. Isselnacher, J. D. Wilson, J. B. Martin, D. L. Kasper, S. L. Hauser, and D. L. Longo (ed.), Harrison's principles of internal medicine, 14th ed. McGraw-Hill, Inc., New York.
Worton, R. G., M. J. Molnar, B. Brais, and G. Karpati. 2001. The muscular dystrophies, p. 5493-5523. In C. R. Scriver, A. L. Beaudet, W. S. Sly, D. Valle, B. Childs, K. W. Kinzler, & B. Vogelstein (ed.), The metabolic and molecular bases of inherited disease, 8th ed. McGraw-Hill, Inc., New York.
Muscle Organization
Tissue
bone, muscle, tendon, and nerve
muscle fiber, myofibril
Filaments
sarcomere
sarcomere (micrograph)
thick and thin filaments (micrograph)
Muscle Organization
(http://www.life.uiuc.edu/crofts/bioph354/images/muscle1.jpg)
Muscle Organization
(http://www.life.uiuc.edu/crofts/bioph354/images/myofib2.jpg)
Muscle Organization
(http://www.life.uiuc.edu/crofts/bioph354/images/sarcom2.jpg)
Muscle Organization
(http://www.life.uiuc.edu/crofts/bioph354/images/sarcomere.jpg)
Muscle Organization
(http://www.life.uiuc.edu/crofts/bioph354/images/sciemyosin3.jpg)
Muscle Proteins
Table of muscle proteins
Table of muscle proteins correlated to diseases
Actin-myosin complex
protein lattice (actin, myosin)
protein lattice (actin, myosin, titin)
power stroke
power stroke (movie)
Dystrophin-associated complex
dystrophin (importance, function)
dystrophin, dystroglycans, and sarcoglycans
correlation to diseases
in situ dystrophin
Striated muscle protein linkages
gross view
sarcomere A-band, I-band, M-line
sarcomere Z-disk
sarcolemma
Muscle Proteins
Location / Protein / Characteristics
Filaments / actin / 42 kDa, polymerizes to 7-nm thin filament
myosin / 540 kDa, forms 15-nm thick filament
troponin / I, C, and T subunits
tropomyosin / 40 nm length
Z disk / a-actinin / 194-kDa dimer
desmin
vimentin
nebulin / spans length of thin filament
titin / 3000 kDa, spans length of thick filament
M line / paramyosin
C-protein / 140 kDa, thick filament in bundles of 200-400
M-protein / 165 kDa
Transmembrane / merosin (laminin-2) / 90 kDa
a-dystroglycan / 153 kDa
b-dystroglycan / 43 kDa
a-sarcoglycan (adhalin) / 50 kDa
b-sarcoglycan / 43 kDa
g-sarcoglycan / 35 kDa
d-sarcoglycan / 35 kDa
sarcospan / ?
Submembrane / dystrophin / 427 kDa
utrophin / 430 kDa
a-syntrophin / 59 kDa
b-1-syntrophin / 59 kDa
b-2-syntrophin / 59 kDa
dystrobrevin / 87 kDa?
Muscle Proteins
(http://www.life.uiuc.edu/crofts/bioph354/images/muscle_fibril.gif)
Muscle Proteins
(http://www.chemsoc.org/exemplarchem/entries/kscott/images/titin.gif)
Muscle Proteins
(http://biochem.annualreviews.org/content/vol68/issue1/images/medium/bi68_0687_1.gif)
Power Stroke
(http://www.sci.sdsu.edu/movies/actin_myosin.html)
Dystrophin Importance
Importance
absent in Duchenne muscular dystrophy (DMD)
reduced or altered in Becker muscular dystrophy (BMD)
deficiency in cardiac-specific form in X-linked dilated cardiomyopathy (XLDC)
Large gene and protein
2500-kb gene
14-kb mRNA (79 exons)
3685 aa
427 kDa
Localization
subsarcolemmal region in skeletal and cardiac muscle
enriched at myotendinous and neuromuscular junctions
associated with T-tubules in cardiac muscle
discontinuous distribution along membrane in smooth muscle, alternates with vinvulin
Dystrophin Function
Protein similarity
a-actinins
spectrins
Functional domains
amino terminus - 240 aa, binds F-actin
coiled-coiled rod - 2400 aa, longest section provides flexibility and elasticity
cysteine-rich - 280 aa, required for membrane attachment to b-dystroglycan
carboxy terminus - 420 aa, contains potential phosphorylation sites, binds to syntrophins
Function
mechanical reinforcement of sarcolemma (in skeletal muscle)
signal transduction (control of muscle fiber caliber and size)
anchor or stabilizer of dystroglycans and sarcoglycans
Dystrophin, Dystroglycans, and Sarcoglycans
(http://med.annualreviews.org/content/vol48/issue1/images/medium/ME48_0457_1.gif)
Correlation to Diseases
(http://www-ermm.cbcu.cam.ac.uk/0200488Xh.htm)
Striated muscle cell proteins implicated in muscular dystrophies, dilated cardiomyopathy and lipodystrophy, and their protein–protein interactions. Myopathies, cardiomyopathy or lipodystrophy known to be caused by particular proteins are indicated in parentheses (red). Spanning the plasma membrane (sarcolemma) of a striated muscle cell (myoblast) is the dystrophin–glycoprotein complex (DGC; bracketed), which provides structural integrity to the cell by crosslinking the cytoskeleton (via actin) to the extracellular matrix (via laminin b1). Mutations in dystrophin cause Duchenne muscular dystrophy (DMD) and mutations in the sarcoglycoproteins cause a variety of limb-girdle muscular dystrophies (LGMD) including 2C, 2D, 2E and 2F. Desmin and actin filaments crosslink the nucleus, sarcomere and sarcolemma. The sarcomere is the structure responsible for muscle contraction, and contains the proteins actin, myosin, titin and telethonin. The muscle LIM protein (MLP; LIM is the term given to a protein–protein interaction domain containing a double zinc finger motif) is a cytoskeletal binding partner of beta-spectrin, itself a cytoskeletal protein. Mutations in lamin A/C can cause LGMD-1B. Other disease abbreviations: AD-EDMD, autosomal dominant Emery–Dreifuss muscular dystrophy; X-EDMD, X-linked EDMD; FPLD, familial Dunnigan-type partial lipodystrophy; CMD, congenital muscular dystrophy; DCM, dilated cardiomyopathy; CMT2, Charcot–Marie–Tooth disorder type 2. The question mark indicates uncertainty as to whether F-actin enters the nucleus from the cytoplasm.
In situ Staining for Dystrophin
(http://www.emedicine.com/neuro/topic670.htm#section~pictures)
Muscle tissue samples are stained with specific antibodies for dystrophin. From left to right, the panels represent (A) normal dystrophin staining; (B) intermediate dystrophin staining in a patient with Becker muscular dystrophy; and (C) absent dystrophin staining in a patient with Duchenne dystrophy.
Cytoskeletal Linkages
(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)
A schematic overview of cytoskeletal linkages in striated muscle (modified from Carlsson & Thornell, 2001). The sarcomeres contain four filament systems: actin-thin, myosin-thick, titin, and nebulin filaments. The borders of individual sarcomeres are the Z-lines, which are precisely aligned and laterally associated with intermediate filament proteins (such as desmin) and other cytoskeletal proteins (such as plectin). The intermediate filaments and associated proteins also may link the peripheral myofibrils to costameres at the sarcolemma (the muscle membrane), to mitochondria, and to the nuclear membrane. Although many of the detailed interactions are not yet known, these linkages are responsible for the mechanical integration and stability of myofibrils, organelles, and membrane components for effective force transmission. The microtubule system is not depicted in the schematic because it is unclear how they are arranged in striated muscle; however, they may be linked to myofibrils and intermediate proteins through proteins such as plakin family members.
Molecular Model of Sarcomere
(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)
Molecular model of the I-band, A-band, and M-line regions of the sarcomere. Polar thin filaments, containing actin, tropomyosin, troponins C, I, and T, and single molecules of skeletal muscle nebulin, span the I-band and interdigitate with the myosin (thick) filaments in the A-band, where they are capped at their pointed ends by tropomodulin. The myosin heads extend from the core of the thick filaments in the C-zone of the A-band, and are anchored and aligned in the middle of the sarcomere, the M-line. Myosin-binding proteins, including MyBP-C, are associated with the thick filaments and likely play multiple roles in the sarcomere. Single molecules of the giant protein titin extend an entire half sarcomere and are proposed to function as a template for sarcomere assembly. Titin's I-band region contains elastic elements that contribute to the passive force of myofibrils. The M-line proteins myomesin and M-protein, as well as MyBP-C, likely contribute to the linkage of thick filaments with titin, whereas MURF-1 and p94 may function in titin M-line region protein turn-over. Also shown here is Novex-3, a novel mini-titin, that binds to another giant protein, obscurin. Other novel titin isoforms have been found that are not shown here. Components whose binding sites are unknown are shown with question marks.
Molecular Model of Sarcomere
(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)
Molecular model of sarcomeric Z-disk components, which form the borders of individual sarcomeres. Opposing thin filaments and individual titin molecules interdigitate at the Z-line and are cross-linked by {alpha}-actinin dimers. The diagram depicts one {alpha}-actinin dimer simultaneously cross-linking two actin filaments and two titin molecules; other configurations are possible. Myopodin and filamin can also bind actin filaments, but it is not clear if they actually cross-link opposing thin filaments, as indicated here. Z-line-associated proteins are shown individually or with known binding partners; the two-dimensional nature of the drawing prevents a full appreciation of how the proteins are arranged with respect to each other. Proteins whose binding sites are unknown are indicated with question marks. It is possible that some Z-line components may be preferentially localized to the Z-line/I-band boundary (e.g., filamin, MLP) or more prominent in the Z-lines of peripheral myofibrils.
Sarcolemma
(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)
A schematic model of the cytoskeletal filament linkages at the sarcolemma of striated muscle. Four major cytoskeletal/membrane junctions are depicted: (a) cadherin-based linkages to actin and intermediate filaments (desmin); (b) integrin-based focal adhesions; (c) dystroglycan complex (DGC); and (d) spectrin-based membrane cytoskeleton. The cadherin-based fascia adheren at the intercalated disc couples neighboring cardiomyocytes (through homotypic interactions) and tethers the contractile apparatus to the muscle termini. Desmosomes are a second cadherin-based junction that anchor desmin filaments at the intercalated disc. Connections between intermediate filament proteins and the membrane may occur through a plectin/{alpha}ß-crystallin complex or via an association with DGC via dystrobrevin. Integrin-based focal adhesions and the DGC act as transmembrane receptors for ECM components (e.g., laminin) and link the extracellular surface with the actin cytoskeleton. Integrins associate with talin, {alpha}-actinin, vinculin and N-RAP to form a strong mechanical link to actin filaments. Integrins could directly interact with {alpha}-actinin and/or other components not depicted here to mediate a connection with actin. The DGC consists of the transmembrane complex {alpha}/ß-dystroglycan, dystrophin, the sarcoglycans, and other components not depicted here. Spectrin is enriched at costameres, and is an important component of the membrane cytoskeleton. It is linked to the membrane through ankyrin and probably the Na,K-ATPase transmembrane protein. Spectrin may have an additional role in anchoring the contractile apparatus to the membrane though an interaction with MLP. Importantly, all of these linkage complexes can bind to the submembraneous actin ({gamma}-actin) and are probably interlinked through this association as well as other unknown interactions.
Metabolic Pathways
Glucose
glycolysis (TCA cycle)
glycogenolysis (TCA cycle)
Fatty acids
b-oxidation (TCA cycle)
Metabolic Pathways
Metabolic Pathways
Metabolic Pathways
Nelson, D. L., and M. M. Cox. 2000. Lehninger principles of biochemistry, 3rd ed., p. 604. Worth Publishers, New York.
Role of Calcium
Muscle contraction
troponin C
Glycogen breakdown
calmodulin (activates phosphorylase b kinase)
Citric acid cycle activation
pyruvate dehydrogenase complex
isocitrate dehydrogenase
a-ketoglutarate dehydrogenase
Role of Calcium