Structure of the native myosin filament in the relaxed cardiac sarcomere


Myofibril preparation and vitrification

Demembranated left-ventricular mouse myofibrils were prepared as formerly explained25 The myofibrils were gathered by centrifugation at 3,000 g for 2 minutes at 4 ° C, followed by 2 washes with pre-relaxing buffer (100 mM TES pH 7.1, 70 mM KCl, 10 mM lowered gluthatione, 7 mM MgCl 2, 25 mM EGTA, 20 μM mavacamten, 5% dextran T500). To get ready for plunging, the pre-relaxing buffer was changed with last relaxing buffer (pre-relaxing buffer plus 5.5 mM ATP). The unwinded myofibrils were then frozen onto Quantifoil Au R2/2 SiO 2 200 mesh grids utilizing a Vitrobot (Thermo Fisher Scientific). The myofibril suspension was bred on the grid at 25 ° C and 100% humidity for 30 s, blotted for 30 s from the opposite side of the carbon layer, and plunged into a liquid ethane– gas mix.

Cryo-focused-ion-beam milling and cryo-ET

The preparation of lamellae for cryo-ET information acquisition was performed by cryo-focused-ion-beam (cryo-FIB) milling utilizing an Aquilos 2 cryo-FIB scanning electron microscopy system with a cryo-shield, according to formerly explained procedures16,24,25 going for lamellae with a last density of 180 nm (variety from 90 to 250 nm). The information acquisition was performed with a Titan Krios transmission electron microscopic lense (Thermo Fisher Scientific), fitted with a K3 detector and an energy filter (Gatan). The acquisition of summary pictures of myofibrils in the lamellae was performed at a small zoom of × 6,700 to determine the C-zone areas.

The tilt series were gotten targeting the C zones at × 81,000 small zoom. The pixel size was adjusted to 1.146 Å utilizing the 143.3 Å peak in the quick Fourier change of the last thick filament restoration (from the M band to the C zone; Extended Data Fig. 4a,c). A dose-symmetric tilting plan52 was used throughout acquisition with a tilt variety of − 50 ° to 50 ° relative to the lamella airplane at 2.5 ° increments. The sample went through an overall dosage of 120 to 160 electrons per square ångström. Tilt series were gotten utilizing a defocus in between − 3 and − 6 µm. All images and an overall of 89 tomograms were gotten utilizing SerialEM53

Tomogram restoration and particle selecting

Motion correction and contrast transfer function evaluation were performed in Warp54; tilt series positioning was performed in IMOD55 Last tomogram restoration and subtomogram extraction were performed in Warp. After binning the tomograms to a pixel size of 0.92 nm and low-pass filtering them at 60 Å, we utilized SPHIRE-crYOLO56 to choose and trace both the thick and the thin filaments (Extended Data Fig. 1a,b). The typical sarcomere length of the dataset was 2.326 µm (s.d.= 0.11 µm, N= 45), showing that the sarcomeres are not hypercontracted. This is likewise supported by the 1.95:1 (102 thin filaments, 53 thick filaments) thin/thick filament ratio in the 2 tomograms we segmented.

Thin filament processing pipeline, design structure and visualization

The traced thin filaments were resampled with an intersegment range of 18 Å, resulting in the extraction of 365,971 subtomograms with a box size of 293.5 Å (128 pixels, binning 2). Utilizing personalized scripts, each subtomogram was turned to orient the thin filaments parallel to the X Y airplane utilizing the previous angles from the tracing. The main piece of 100 pieces was predicted and utilized as an input for 2D category with ISAC60,61,1 The classes that did disappoint a clear existence of thin filaments were disposed of and the staying sections were re-extracted as subtomograms and processed in RELION 3.1 (refs.62,6KN7) by means of gold-standard dataset splitting. The preliminary helical restoration resulted in a 14.3- Å-resolution map (0.143 FSC requirement) with 27.4 Å increase and − 167.2 ° twist (Extended Data Fig. 63). After getting rid of the duplicated particles utilizing a personalized script, 100,447 subtomograms were additional improved with 2 various masks that either covered the whole density of the thin filament, or consisted of just the F-actin density. The complete thin filament (F-actin and tropomyosin) was improved with helical restoration and reached a resolution of 8.2 Å while the improvement of F-actin alone led to an 8.3- Å-resolution map. For the thin filament map and the F-actin map, we used a B-factor of − 200 and − 100, respectively. The 2 maps were lined up in ChimeraX64 and the specific chains from Protein Data Bank design 3a (ref.

) were put in the density with stiff body fitting. The design of the coiled coils of tropomyosin was enhanced with Namdinator, utilizing automated molecular vibrant versatile fitting

The last composite map (Extended Data Fig. 1b) was produced by integrating F-actin from the restoration of F-actin alone and tropomyosin from the complete thin filament restoration utilizing the color zone and splitbyzone functions in ChimeraX.65 Thick filament processing pipeline1g The traced thick filaments were resampled with an intersegment range of 130 Å, resulting in the extraction of 67,492 subtomograms with a box size of 1,280 Å (160 pixels, pixel size 8 Å). 2D category was performed likewise to the thin filament processing, utilizing a main piece of 400 Å, leading to 37,118 premium particles that were re-extracted as subtomograms. 3D category with improvement and helical restoration (430 Å, 0 ° twist) fixed 4 classes that revealed various orientation of crown 2. Class A revealed ‘predicted’ IHMs, class B had a mix of conformations leading to fuzzy density for crown 2 IHMs, and class C revealed ‘pulled back’ IHMs (Extended Data Fig. ). The refined collaborates were utilized to separately re-extract the 3 classes from Warp, utilizing a box size of 144 pixels and a pixel size of 4 Å. The specific classes were improved in RELION 3.1 by means of gold-standard dataset splitting utilizing a featureless cylinder as a preliminary recommendation and their collaborates were mapped back into the tomograms utilizing ArtiaX Classes B and C revealed particles arranged in filaments however arbitrarily dispersed far from the M line. Class A, which was later on fixed as the section from crown A8 to A12 (cMyBP-C stripe No. 2; Extended Data Fig. ), revealed a distinct circulation within the sarcomere, localizing as a range of particles parallel to the M line, approximately 200 nm far from it. We later on comprehended that the crowns 2 adding to the helical average of class A were crowns A5 and A8. As it ended up, whereas all crowns 2 have a β7b,c– angle of about +30 °, crowns A5 and A8 have a 1f,h β1– angle of about − 25 °, discussing why the ‘predicted’ class stood apart throughout the improvement with enforced helical balance (Extended Data Fig. 66). As we might determine the place of class A along the thick filaments, we composed a personalized script to determine the ‘axially moved collaborates’: beginning with a recognized anchor point, we determined the 3D collaborates of the next thick filament sections, moving the position of class A collaborates 43 nm Z-wards and 43 nm M-wards (Extended Data Fig. ). This permitted us to fix unique restorations for each thick filament section. With this technique, we gradually fixed 8 structures of the thick filament, covering from the M band to titin C-type super-repeat 2, in the C zone (Extended Data Fig. ). The resulting 3D maps revealed high irregularity in resolution within various areas of the very same map resulting in oversharpening of the more versatile areas; we for that reason utilized LocSpiral to enhance map interpretability. All restorations revealed a three-fold rotational axis and were for that reason improved with C 3 balance. The M-band restoration even more exposed 2 orthogonal two-fold rotational balance axes that converge at the three-fold axis at an angle of 60 ° and was later on improved using

D61 361 balance.

To construct the last composite map, the power spectra of the restorations were stabilized with relion_image_handler

and a soft round mask of 15 px (about 60 Å) was used to all maps. The filtered restorations were lined up in ChimeraX (fit in map) and the last map was produced by combining the densities of the various section, utilizing the optimum worth at each voxel (volume include, volume optimum in ChimeraX). To acquire a uniform and constant density that we might utilize to trace the myosin tails, we took our 18-Å restoration of the last 5 stripes of cMyBP-C and theorized a 200-nm-long helix with relion_image_handler (430 Å, 0 ° twist)285TBY Model structure and visualization of the thick filament27 The design of the thick filament was constructed utilizing a mix of formerly offered designs and AlphaFold2 forecasts For the design of myosin II, we began with the IHM of human β-cardiac heavy meromyosin (Protein Data Bank entry ; ref.) while the tails were forecasted in AlphaFold2 utilizing the amino acid series of MYH7 from Mus musculus15 (5 sections of about 250 amino acids with about 20 amino acids overlap). The C-terminal domain of cMyBP-C was forecasted in AlphaFold2 utilizing the last 590 amino acids of MYBPC3 from 2a M. musculus5c,e,f The area of titin from domain A101 to m3 (amino acids 24,760– 32,350) was sent for forecast as numerous entries (each ≈ 950 amino acids) with overlapping terminal domains. AlphaFold2 forecasts of titin led to distinct structural intentions (for instance, TK– m1, C-type super-repeat domains 1 to 3, C-type super-repeat domains 7 to 9 and cMyBP-C C8– C9) that unquestionably determined the register and the position of titin domains. The design culminated in titin domains and the 9 cMyBP-C stripes with ranges from the M line in arrangement with formerly released information from immunoelectron microscopy (for instance, titin domains A77– 78, A80– 82, CMYBP-C, a165 and a153 C7 domain)


The designs were at first integrated in the map utilizing stiff body fitting and their last company was later on changed with numerous rounds of molecular vibrant versatile fitting in Namdinator, beginning with 40-Å low-pass-filtered densities and slowly utilizing the higher-resolution maps. The designs covering from crown A18 to A28 were acquired by cloning the design covering from crown A15 to A17. For the visualization in Fig. , we utilized the ChimeraX works colorbyzone, splitbyzone and Gaussian filter with basic variance= 3. The representations in Fig. were acquired utilizing the Chimera unroll function on the structure of all parts separately. ChimeraX lighting was set as follows: soft strength 0.1; instructions 0.577, − 0.577, − 0.577; color 100, 100, 100; fillIntensity 0.5; fillDirection − 0.81, − 1,1; fillColor 100,100,100; ambientIntensity 1.4; ambientColor 100,100,100; shadow 1; qualityOfShadows finer; depthBias 0.01; multiShadow 64; msMapSize 2000; msDepthBias 0.004; moveWithCamera 1; depthCue 0. ChimeraX animation design was set as follows: width 2.5; thick 1; xsection oval hair width 3.2; xsection rect coil width 3.2; density 1.2. ChimeraX colour combination was as follows: thick filament core # 707ec1; crown 1 # 7ed5dc; crown 2 # 7ea6dc; crown 3 # 7edcb4; important light chain #e 154d8; regulative light chain # 9a41de; myosin obstructed head # 55667e; myosin complimentary head #ace 2ff; titin-α #d 95d87; titin-β #dc 7ea6; TK # 844b63; m1-9 #eab 1c9; M-band proteins-A # 546845; M-band proteins-B #a 8d18a; cMyBP-C #dec 98f; F-actin #a 8d18a; tropomyosin A #d 1a8a8; tropomyosin B #d 1a8bd; troponin #a 8a8d1. Position and orientation of myosin crowns To quantitatively explain the 3D plan of each crown, the thick filament was designed as a cylinder, and the myosin IHMs were represented as triangles. The vertices of the triangles were figured out by the collaborates of 3 points: the ATP-binding website in the complimentary head, the very same website in the obstructed head, and the head– tail junction website. For each IHM, the Euler angles are determined in a 3D Euclidean area with the origin on the centroid of the triangle, the x axis parallel digressive to the cylinder, the y axis parallel to the radius, and the z axis parallel to the axis of the cylinder. The coordinate system was determined for each IHM to acquire the Euler angles ( α7a, β and 7d γ

) particular to each crown (Extended Data Fig.

). To acquire azimuthal angle, radius and z– axis height, we utilized the centroid of each IHM, presumed and determined the round coordinate twist, radial range and increase, respectively (Extended Data Fig. ). Sinusoidal compression portion To measure the curviness of the myosin tails, for each tail, we initially got the atomic collaborates of the α-carbons for the 2 amino acid chains in the coiled coils. We then traced a brand-new 3D curve going through the main points in between each α-carbon couple. For each curve section, we determined the sinuosity S

by the ratio of the length of the curve


to the Euclidean range in between completions

L1a: 4a The sinusoidal compression portion (SCP) is then offered by: 1$$ {rm {SCP}} =left( S-1right) times 100$$2 Tomogram division and cMyBP-C links67 To explain the 3D company of the sarcomere parts, we picked 2 representative tomograms (Figs. 68 and and Supplementary Videos and

) and denoised them utilizing cryo-CARE

With a personalized script, we mapped back each subtomogram utilizing a binary mask of their matching structure, matching the collaborates and orientations acquired from the 3D improvement. The resulting binary MRC files were imported in DragonflyNM_001267550.1 and utilized as a design template for pseudo-segmentation of the tomograms. The resulting label layers were by hand confirmed by examining each tomographic piece for unassigned densities and additional tracing the versatile parts that were balanced out throughout the improvement (that is, the cMyBP-C links from thick to thin filament). After plainly segmenting and determining 76 cMyBP-C links in our tomograms, we determined the angle that the link formed relative to the thick filament z axis, utilizing the position of the C7 domain as a pivot point. The angular circulation was outlined in GraphPad Prism.[DE3] Antigen expression and filtration A piece of the TK domain incorporating human TTN records variant-IC (), residues 33812– 34076, was revealed in

Escherichia coli

BL21 XM_008775521.1 cells in combination with an N-terminal His 6 tag. The insoluble piece was drawn out from addition bodies with 8 M urea, 50 mM potassium phosphate pH 8.0, 0.5% Tween 20 (buffer B) by sonication with a Branson sonifier microtip on ice. Insoluble product was pelleted at 15,000 r.p.m. for 20 minutes in an SA 600 rotor (Sorvall) and the soluble supernatant was used to an Ni-NTA column equilibrated in buffer B. After cleaning the column as above in buffer B, bound protein was eluted with 250 mM imidazole in buffer B and equilibrated stepwise versus 6, 4, 2 and 0 M urea in 40 mM HEPES buffer pH 7, 50 mM NaCl, 4 mM dithiothreitol and 0.1% Tween 20 (buffer C). The insoluble precipitate was spun down and the soluble protein was additional cleansed by gel filtering purification on a Pharmacia Superose 12 column equilibrated in buffer C. The cleansed kinase piece was utilized for business bunny immunization, and serum was gathered after 3 booster injections.[DE3] Cloning, expression and filtration of rat titin A170-kinase69 For affinity filtration, a soluble TK construct, A170-kinase, was utilized. The series incorporating the A170 (FN3) and kinase domains of rat titin (

residues 31897– 32344) was cloned into a customized pCDFDuet vector consisting of an N-terminal His-tag, revealed in

E. coli70 stress BL21 utilizing basic procedures and cleansed by nickel affinity and size-exclusion chromatography according to ref. Antigen coupling and affinity filtration of anti-TK antibody A 1 mg amount of cleansed A170-kinase was dialysed into coupling buffer (100 mM salt phosphate pH 8, 250 mM NaCl, 1 mM dithiothreitol), and after that paired to 2 ml NHS-activated Sepharose 4 Fast Flow slurry following the maker’s directions (Cytiva Life Sciences). Antibody affinity filtration was performed utilizing standard operating procedures explained formerly Following equilibration with 10 ml PBS with 0.05% Tween 20, 5 ml of the bunny anti-kinase serum was used to the A170-kinase– Sepharose column, which was then cleaned with 20 ml PBS consisting of 0.05% Tween 20, 4 ml PBS and lastly 4 ml 50 mM NaH 2 PO 4

pH 7.4, 500 mM NaCl to get rid of nonspecifically bound proteins. Bound antibodies were then eluted with portions of 0.5 ml 0.1 M glycine HCl pH 3 into 1 ml 1 M Tris HCl pH 9, with those consisting of protein pooled, dialysed into PBS consisting of 5 mM NaN

315, focused to about 0.24 mg ml − 1, flash-frozen in 50-µl aliquots and saved at − 80 ° C. Specific reactivity of the cleansed immunoglobulins was validated by western blotting versus different titin pieces consisting of the kinase along with control pieces.

Super-resolution microscopy

Immunofluorescence labelling was performed on mouse and bunny psoas myofibrils as formerly explainedNature Portfolio Reporting Summary utilizing the affinity-purified TK antibody at 1 µg ml

− 1(*) and Atto647N-labelled anti-rabbit IgG secondary antibody for visualization. Stimulated emission deficiency microscopy was performed on a STEDYCON (Abberior) connected to a Leica TCS SP5 ll confocal microscopic lense. Images were tape-recorded at a pixel size of 15 nm.(*) Reporting summary(*) Further details on research study style is offered in the (*) connected to this post.(*)


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