muscle biochemistryeniederhoffer/som_pbl/nmb/musc_bioch/musc_bi… · niederhoffer muscle...

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Muscle Biochemistry

Eric C. Niederhoffer, Ph.D.Associate Professor, Biochemistry & Molecular Biology

Copyright 2001-2004, E.C. Niederhoffer. All Rights Reserved.All trademarks and copyrights are the property of their respective owners.

OverviewResources (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)

Niederhoffer Muscle Biochemistry C2000

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ResourcesNeuromuscular 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 musculardystrophies, 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.


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Muscle OrganizationTissuebone, muscle, tendon, and nerve

muscle fiber, myofibril

Filamentssarcomere

sarcomere (micrograph)

thick and thin filaments (micrograph)

Muscle Organization

(http://www.life.uiuc.edu/crofts/bioph354/images/muscle1.jpg)


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Muscle Organization

(http://www.life.uiuc.edu/crofts/bioph354/images/myofib2.jpg)

Muscle Organization

(http://www.life.uiuc.edu/crofts/bioph354/images/sarcom2.jpg)


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Muscle Organization

(http://www.life.uiuc.edu/crofts/bioph354/images/sarcomere.jpg)

Muscle Organization

(http://www.life.uiuc.edu/crofts/bioph354/images/sciemyosin3.jpg)


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Muscle ProteinsTable of muscle proteinsTable of muscle proteins correlated to diseasesActin-myosin complexprotein lattice (actin, myosin)

protein lattice (actin, myosin, titin)

power stroke

power stroke (movie)

Dystrophin-associated complexdystrophin (importance, function)

dystrophin, dystroglycans, and sarcoglycans

correlation to diseases

in situ dystrophin

Striated muscle protein linkagesgross view

sarcomere A-band, I-band, M-line

sarcomere Z-disk

sarcolemma


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Muscle ProteinsLocation Protein Characteristics

actin 42 kDa, polymerizes to 7-nm thin filament

myosin 540 kDa, forms 15-nm thick filament

troponin I, C, and T subunits

Filaments

tropomyosin 40 nm length

α-actinin 194-kDa dimer

desmin

vimentin

nebulin spans length of thin filament

Z disk

titin 3000 kDa, spans length of thick filament

paramyosin

C-protein 140 kDa, thick filament in bundles of 200-400M line

M-protein 165 kDa

merosin (laminin-2) 90 kDa

α-dystroglycan 153 kDa

β-dystroglycan 43 kDa

α-sarcoglycan (adhalin) 50 kDa

β-sarcoglycan 43 kDa

γ-sarcoglycan 35 kDa

δ-sarcoglycan 35 kDa

Transmembrane

sarcospan ?

dystrophin 427 kDa

utrophin 430 kDa

α-syntrophin 59 kDa

β-1-syntrophin 59 kDa

β-2-syntrophin 59 kDa

Submembrane

dystrobrevin 87 kDa?


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Muscle Proteins

(http://www.life.uiuc.edu/crofts/bioph354/images/muscle_fibril.gif)


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Muscle Proteins

(http://www.chemsoc.org/exemplarchem/entries/kscott/images/titin.gif)


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Muscle Proteins

(http://biochem.annualreviews.org/content/vol68/issue1/images/medium/bi68_0687_1.gif)


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Power Stroke

(http://www.sci.sdsu.edu/movies/actin_myosin.html)


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Dystrophin ImportanceImportanceabsent 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 protein2500-kb gene

14-kb mRNA (79 exons)

3685 aa

427 kDa

Localizationsubsarcolemmal 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 FunctionProtein similarityα-actinins

spectrins

Functional domainsamino 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 β-dystroglycan

carboxy terminus - 420 aa, contains potential phosphorylation sites, binds to syntrophins

Functionmechanical reinforcement of sarcolemma (in skeletal muscle)

signal transduction (control of muscle fiber caliber and size)

anchor or stabilizer of dystroglycans and sarcoglycans


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Dystrophin, Dystroglycans, and Sarcoglycans

(http://med.annualreviews.org/content/vol48/issue1/images/medium/ME48_0457_1.gif)


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Correlation to Diseases

(http://www-ermm.cbcu.cam.ac.uk/0200488Xh.htm)Striated muscle cell proteins implicated in muscular dystrophies, dilated cardiomyopathy andlipodystrophy, 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 proteinsactin, 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 partnerof 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-linkedEDMD; 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.


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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 toright, the panels represent (A) normal dystrophin staining; (B) intermediate dystrophinstaining in a patient with Becker muscular dystrophy; and (C) absent dystrophin stainingin a patient with Duchenne dystrophy.


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Cytoskeletal Linkages

(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)

A schematic overview of cytoskeletal linkages in striated muscle (modified fromCarlsson & Thornell, 2001). The sarcomeres contain four filament systems: actin-thin,myosin-thick, titin, and nebulin filaments. The borders of individual sarcomeres are theZ-lines, which are precisely aligned and laterally associated with intermediate filamentproteins (such as desmin) and other cytoskeletal proteins (such as plectin). Theintermediate filaments and associated proteins also may link the peripheral myofibrils tocostameres at the sarcolemma (the muscle membrane), to mitochondria, and to thenuclear membrane. Although many of the detailed interactions are not yet known, theselinkages are responsible for the mechanical integration and stability of myofibrils,organelles, and membrane components for effective force transmission. The microtubulesystem 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 proteinsthrough proteins such as plakin family members.


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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 thinfilaments, containing actin, tropomyosin, troponins C, I, and T, and single molecules ofskeletal 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 likelyplay multiple roles in the sarcomere. Single molecules of the giant protein titin extend anentire 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, likelycontribute to the linkage of thick filaments with titin, whereas MURF-1 and p94 mayfunction in titin M-line region protein turn-over. Also shown here is Novex-3, a novelmini-titin, that binds to another giant protein, obscurin. Other novel titin isoforms havebeen found that are not shown here. Components whose binding sites are unknown areshown with question marks.


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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 individualsarcomeres. 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 arearranged with respect to each other. Proteins whose binding sites are unknown areindicated 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 moreprominent in the Z-lines of peripheral myofibrils.


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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 intermediatefilaments (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 themuscle 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 occurthrough 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. TheDGC 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 ofthe 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 thesubmembraneous actin ({gamma}-actin) and are probably interlinked through this association as well as

other unknown interactions.


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Metabolic PathwaysGlucoseglycolysis (TCA cycle)

glycogenolysis (TCA cycle)

Fatty acidsβ-oxidation (TCA cycle)

Metabolic Pathways


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Metabolic Pathways


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Metabolic Pathways

Nelson, D. L., and M. M. Cox. 2000. Lehninger principles of

biochemistry, 3rd ed., p. 604. Worth Publishers, New York.


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Role of CalciumMuscle contractiontroponin C

Glycogen breakdowncalmodulin (activates phosphorylase b kinase)

Citric acid cycle activationpyruvate dehydrogenase complex

isocitrate dehydrogenase

α-ketoglutarate dehydrogenase

Role of Calcium

muscle biochemistryeniederhoffer/som_pbl/nmb/musc_bioch/musc_bi… · niederhoffer muscle...

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