{"format":"molecular-machines.cards","version":1,"updated":"2026-10-01","decks":[{"machine":"myosin","name":"Myosin","count":28,"url":"/learn/cards/myosin.json"}],"cards":[{"id":"myosin-class-differences","machine":"myosin","kind":"qa","prompt":"Myosin classes share the same head. Name the three things that differ between them.","answer":"Lever length, direction, and time spent bound to actin.","explanation":"Across isoforms the motor-domain states are nearly invariant; the lever position differs.","section":"summary","topic":"purpose","sources":["machine:summary","evolution:Variable lever","ref:houdusse2000"],"tags":["classes","lever"],"difficulty":2,"url":"/machines/myosin#summary","cites":[{"source":"machine:summary","machine":"myosin","label":"Summary","section":"summary"},{"source":"evolution:Variable lever","machine":"myosin","label":"Variable lever","section":"summary"},{"source":"ref:houdusse2000","machine":"myosin","label":"Houdusse et al.","section":"sources","anchor":"ref-houdusse2000","href":"https://doi.org/10.1073/pnas.200376897"}]},{"id":"myosin-converter-lever-role","machine":"myosin","kind":"qa","prompt":"In a myosin head, what does the long lever-arm helix do with the rotation of the converter?","answer":"It amplifies the rotation into a stroke.","explanation":"The converter turns with the motor state; the lever turns that small turn into a large stroke, so lever length sets the stroke.","section":"summary","topic":"parts","sources":["component:converter and lever arm"],"tags":["lever","converter"],"difficulty":1,"url":"/machines/myosin#summary","cites":[{"source":"component:converter and lever arm","machine":"myosin","label":"Part: converter and lever arm","section":"summary"}]},{"id":"myosin-tail-role","machine":"myosin","kind":"qa","prompt":"What does the coiled-coil tail of myosin do?","answer":"It joins the two heavy chains and builds thick filaments or binds cargo.","explanation":"The head does the work on actin; the tail decides what the pull is applied to.","section":"summary","topic":"parts","sources":["component:coiled-coil tail"],"tags":["tail","cargo"],"difficulty":1,"url":"/machines/myosin#summary","cites":[{"source":"component:coiled-coil tail","machine":"myosin","label":"Part: coiled-coil tail","section":"summary"}]},{"id":"myosin-duty-ratio-definition","machine":"myosin","kind":"qa","prompt":"What is the duty ratio of a myosin head?","answer":"The fraction of the cycle it spends strongly bound to actin.","explanation":"Myosin-5 has a duty ratio of about 0.7; muscle myosin spends only a small fraction of its cycle bound.","section":"summary","topic":"numbers","sources":["stat:Duty ratio, myosin-5","evolution:Duty ratio and function","ref:delacruz1999"],"tags":["duty-ratio"],"difficulty":1,"url":"/machines/myosin#summary","cites":[{"source":"stat:Duty ratio, myosin-5","machine":"myosin","label":"Key number: Duty ratio, myosin-5","section":"summary"},{"source":"evolution:Duty ratio and function","machine":"myosin","label":"Duty ratio and function","section":"summary"},{"source":"ref:delacruz1999","machine":"myosin","label":"De La Cruz et al.","section":"sources","anchor":"ref-delacruz1999","href":"https://doi.org/10.1073/pnas.96.24.13726"}]},{"id":"myosin-muscle-low-duty","machine":"myosin","kind":"qa","prompt":"Muscle myosin spends only a small fraction of its cycle bound to actin. How does muscle still pull steadily?","answer":"Its heads work in large ensembles.","explanation":"Each thick filament carries about 300 myosins. Only a few hold on at any moment; each pulls, lets go and grabs again.","section":"summary","topic":"numbers","sources":["stat:Duty ratio, myosin-5","stop:filament","ref:delacruz1999"],"tags":["duty-ratio","muscle"],"difficulty":2,"url":"/machines/myosin#summary","cites":[{"source":"stat:Duty ratio, myosin-5","machine":"myosin","label":"Key number: Duty ratio, myosin-5","section":"summary"},{"source":"stop:filament","machine":"myosin","label":"Big picture: The thick filament","section":"story"},{"source":"ref:delacruz1999","machine":"myosin","label":"De La Cruz et al.","section":"sources","anchor":"ref-delacruz1999","href":"https://doi.org/10.1073/pnas.96.24.13726"}]},{"id":"myosin-cardiac-drugs-pocket","machine":"myosin","kind":"qa","prompt":"Omecamtiv mecarbil activates cardiac myosin and mavacamten inhibits it. What do the two drugs have in common at the structure level?","answer":"They bind the same pocket.","explanation":"Structures of this shared pocket support rational design of the next cardiac myosin drugs.","section":"summary","topic":"debate","sources":["species:Beta-cardiac myosin","frontier:Cardiac myosin drugs","ref:auguin2024"],"tags":["drugs","heart"],"difficulty":2,"url":"/machines/myosin#summary","cites":[{"source":"species:Beta-cardiac myosin","machine":"myosin","label":"Beta-cardiac myosin","section":"summary"},{"source":"frontier:Cardiac myosin drugs","machine":"myosin","label":"Open question: Cardiac myosin drugs","section":"summary"},{"source":"ref:auguin2024","machine":"myosin","label":"Auguin et al.","section":"sources","anchor":"ref-auguin2024","href":"https://doi.org/10.1038/s41467-024-47587-9"}]},{"id":"myosin-cardiac-drug-approved","machine":"myosin","kind":"cloze","prompt":"Both cardiac myosin drugs completed phase 3 trials, and regulators have approved {{mavacamten}}.","answer":"mavacamten","explanation":"Mavacamten, first reported as MYK-461, lowers the ATPase of cardiac myosin.","section":"summary","topic":"debate","sources":["frontier:Cardiac myosin drugs","ref:green2016"],"tags":["drugs","heart"],"difficulty":2,"url":"/machines/myosin#summary","cites":[{"source":"frontier:Cardiac myosin drugs","machine":"myosin","label":"Open question: Cardiac myosin drugs","section":"summary"},{"source":"ref:green2016","machine":"myosin","label":"Green et al.","section":"sources","anchor":"ref-green2016","href":"https://doi.org/10.1126/science.aad3456"}]},{"id":"myosin-cleft-gates-phosphate","machine":"myosin","kind":"qa","prompt":"When a primed myosin head first docks on actin, why can phosphate not leave yet?","answer":"The actin-binding cleft is still open.","explanation":"Contacts with the actin N-terminus rotate the upper 50-kDa subdomain and close the cleft; only then can phosphate leave and the head bind strongly.","section":"mechanism","topic":"cycle","sources":["mechanism:A primed head docks on actin","mechanism:The cleft closes and phosphate leaves","ref:klebl2025"],"tags":["phosphate","cleft"],"difficulty":2,"url":"/machines/myosin#mechanism","cites":[{"source":"mechanism:A primed head docks on actin","machine":"myosin","label":"Step: A primed head docks on actin","section":"mechanism"},{"source":"mechanism:The cleft closes and phosphate leaves","machine":"myosin","label":"Step: The cleft closes and phosphate leaves","section":"mechanism"},{"source":"ref:klebl2025","machine":"myosin","label":"Klebl et al.","section":"sources","anchor":"ref-klebl2025","href":"https://doi.org/10.1038/s41586-025-08876-5"}]},{"id":"myosin-power-stroke-angle","machine":"myosin","kind":"cloze","prompt":"In the myosin power stroke, the converter rotates and the lever swings through about {{93 degrees}}, mostly along the filament.","answer":"93 degrees","explanation":"Measured for myosin-5 on actin by time-resolved cryo-EM. Because the swing runs along the filament, nearly all of it moves the load forward.","section":"mechanism","topic":"cycle","sources":["mechanism:The power stroke","stat:Lever swing on actin","ref:klebl2025"],"tags":["power-stroke","lever"],"difficulty":2,"url":"/machines/myosin#mechanism","cites":[{"source":"mechanism:The power stroke","machine":"myosin","label":"Step: The power stroke","section":"mechanism"},{"source":"stat:Lever swing on actin","machine":"myosin","label":"Key number: Lever swing on actin","section":"summary"},{"source":"ref:klebl2025","machine":"myosin","label":"Klebl et al.","section":"sources","anchor":"ref-klebl2025","href":"https://doi.org/10.1038/s41586-025-08876-5"}]},{"id":"myosin-atp-releases-why","machine":"myosin","kind":"qa","prompt":"Why does ATP binding make a myosin head let go of actin?","answer":"A head cannot hold both ATP and actin tightly, so the actin-binding cleft opens.","explanation":"Pospich and colleagues call ATP binding and actin binding reciprocal. The transducer links the pocket to the cleft.","section":"mechanism","topic":"cycle","sources":["step:The rear head lets go","mechanism:ATP frees the head","ref:pospich2021"],"tags":["atp","cleft"],"difficulty":3,"url":"/machines/myosin#mechanism","cites":[{"source":"step:The rear head lets go","machine":"myosin","label":"Step: The rear head lets go","section":"mechanism"},{"source":"mechanism:ATP frees the head","machine":"myosin","label":"Step: ATP frees the head","section":"mechanism"},{"source":"ref:pospich2021","machine":"myosin","label":"Pospich et al.","section":"sources","anchor":"ref-pospich2021","href":"https://doi.org/10.7554/eLife.73724"}]},{"id":"myosin-recovery-stroke","machine":"myosin","kind":"qa","prompt":"What does a myosin head do during the recovery stroke, off actin?","answer":"It swings its lever back and hydrolyses ATP, holding ADP and phosphate in the primed state.","explanation":"This re-cocks the lever, so the head is ready for its next power stroke.","section":"mechanism","topic":"cycle","sources":["mechanism:Recovery stroke off actin","ref:houdusse1999"],"tags":["recovery-stroke","atp"],"difficulty":2,"url":"/machines/myosin#mechanism","cites":[{"source":"mechanism:Recovery stroke off actin","machine":"myosin","label":"Step: Recovery stroke off actin","section":"mechanism"},{"source":"ref:houdusse1999","machine":"myosin","label":"Houdusse et al.","section":"sources","anchor":"ref-houdusse1999","href":"https://doi.org/10.1016/S0092-8674(00)80756-4"}]},{"id":"myosin-myosin5-pace-step","machine":"myosin","kind":"qa","prompt":"Which step sets the walking pace of myosin-5?","answer":"ADP release from the rear head.","explanation":"ADP leaves at 11.7 per second, close to the whole ATPase rate of 12–15 per second.","section":"mechanism","topic":"cycle","sources":["step:ADP leaves the rear head","evidence:delacruz1999-adp-release","ref:delacruz1999"],"tags":["adp","myosin-5","kinetics"],"difficulty":2,"url":"/machines/myosin#mechanism","cites":[{"source":"step:ADP leaves the rear head","machine":"myosin","label":"Step: ADP leaves the rear head","section":"mechanism"},{"source":"evidence:delacruz1999-adp-release","machine":"myosin","label":"ADP release from actomyosin V compared with the ATPase rate (De La Cruz EM 1999)","section":"evidence","anchor":"ev-delacruz1999-adp-release"},{"source":"ref:delacruz1999","machine":"myosin","label":"De La Cruz et al.","section":"sources","anchor":"ref-delacruz1999","href":"https://doi.org/10.1073/pnas.96.24.13726"}]},{"id":"myosin-myosin5-why-bound","machine":"myosin","kind":"qa","prompt":"Why does a single myosin-5 head spend about 70% of its cycle strongly bound to actin?","answer":"Its slowest step, ADP release, happens while it is strongly bound.","explanation":"A high duty ratio lets a two-headed myosin-5 keep one head on actin while the other steps.","section":"mechanism","topic":"cycle","sources":["step:ADP leaves the rear head","evidence:delacruz1999-duty-ratio","ref:delacruz1999"],"tags":["duty-ratio","myosin-5"],"difficulty":3,"url":"/machines/myosin#mechanism","cites":[{"source":"step:ADP leaves the rear head","machine":"myosin","label":"Step: ADP leaves the rear head","section":"mechanism"},{"source":"evidence:delacruz1999-duty-ratio","machine":"myosin","label":"Fraction of single-headed myosin V strongly bound to actin during ATP turnover (De La Cruz EM 1999)","section":"evidence","anchor":"ev-delacruz1999-duty-ratio"},{"source":"ref:delacruz1999","machine":"myosin","label":"De La Cruz et al.","section":"sources","anchor":"ref-delacruz1999","href":"https://doi.org/10.1073/pnas.96.24.13726"}]},{"id":"myosin-myosin5-13-subunits","machine":"myosin","kind":"qa","prompt":"Why do the two heads of myosin-5 bind actin 13 subunits apart?","answer":"A site 13 subunits on faces the same way, so the motor walks straight.","explanation":"Actin repeats its pattern about every 36 nm; 13 subunits at about 2.75 nm each is about 36 nm, the step of myosin-5.","section":"mechanism","topic":"cycle","sources":["step:Both heads hold actin","evidence:walker2000-head-span","ref:walker2000"],"tags":["actin","myosin-5","step"],"difficulty":3,"url":"/machines/myosin#mechanism","cites":[{"source":"step:Both heads hold actin","machine":"myosin","label":"Step: Both heads hold actin","section":"mechanism"},{"source":"evidence:walker2000-head-span","machine":"myosin","label":"Axial distance between the two heads of myosin V bound to actin (Walker ML 2000)","section":"evidence","anchor":"ev-walker2000-head-span"},{"source":"ref:walker2000","machine":"myosin","label":"Walker et al.","section":"sources","href":"https://doi.org/10.1038/35015592"}]},{"id":"myosin-myosin5-lead-held","machine":"myosin","kind":"qa","prompt":"In a two-headed myosin-5 on actin, what holds the lead head's lever in the primed position after it releases phosphate?","answer":"The pull from the rear head.","explanation":"The lead head waits with ADP until the rear head lets go; then nothing holds its lever back and it swings.","section":"mechanism","topic":"cycle","sources":["step:The new lead head releases phosphate","step:The lead head swings its lever","ref:klebl2025"],"tags":["myosin-5","strain"],"difficulty":3,"url":"/machines/myosin#mechanism","cites":[{"source":"step:The new lead head releases phosphate","machine":"myosin","label":"Step: The new lead head releases phosphate","section":"mechanism"},{"source":"step:The lead head swings its lever","machine":"myosin","label":"Step: The lead head swings its lever","section":"mechanism"},{"source":"ref:klebl2025","machine":"myosin","label":"Klebl et al.","section":"sources","anchor":"ref-klebl2025","href":"https://doi.org/10.1038/s41586-025-08876-5"}]},{"id":"myosin-muscle-layout","machine":"myosin","kind":"qa","prompt":"In muscle, how do myosins add their forces, and how do sarcomeres add their shortening?","answer":"Myosins sit side by side, so forces add; sarcomeres sit end to end, so shortenings add.","explanation":"This layout turns strokes of a few nanometres into movements of centimetres.","section":"story","topic":"purpose","sources":["story:summary"],"tags":["muscle","sarcomere"],"difficulty":2,"url":"/machines/myosin#story","cites":[{"source":"story:summary","machine":"myosin","label":"Big picture","section":"story"}]},{"id":"myosin-train-analogy-breaks","machine":"myosin","kind":"qa","prompt":"Muscle is like train carriages coupled in a row. What does this analogy get wrong about the sarcomere?","answer":"Nothing in a sarcomere shrinks; the filaments slide past each other.","explanation":"The analogy is right that units in series add their travel and units side by side add their force.","section":"story","topic":"purpose","sources":["analogy:Train carriages coupled in a row","stop:sarcomere"],"tags":["analogy","sarcomere"],"difficulty":2,"url":"/machines/myosin#story","cites":[{"source":"analogy:Train carriages coupled in a row","machine":"myosin","label":"Analogy: Train carriages coupled in a row","section":"story"},{"source":"stop:sarcomere","machine":"myosin","label":"Big picture: The sarcomere","section":"story"}]},{"id":"myosin-rowing-analogy-breaks","machine":"myosin","kind":"qa","prompt":"Myosin heads are like a rowing crew. Where does this analogy break down?","answer":"Rowers pull in time; each myosin head works on its own clock.","explanation":"Each head also lets go of actin for most of its cycle, so only a few hold on at any moment.","section":"story","topic":"purpose","sources":["analogy:A rowing crew"],"tags":["analogy","duty-ratio"],"difficulty":2,"url":"/machines/myosin#story","cites":[{"source":"analogy:A rowing crew","machine":"myosin","label":"Analogy: A rowing crew","section":"story"}]},{"id":"myosin-gain-to-hand","machine":"myosin","kind":"cloze","prompt":"From the phosphate in a myosin head to the hand, movement grows about {{30 million}} times.","answer":"30 million","explanation":"About 0.5 nm at the active site becomes about 15 mm at the hand, through the lever, many heads, sarcomeres in a row and the arm (human biceps estimate).","section":"story","topic":"numbers","sources":["fact:M9","ref:bnid107902"],"tags":["scale","gain"],"difficulty":2,"url":"/machines/myosin#story","cites":[{"source":"fact:M9","machine":"myosin","label":"Gain from the phosphate to the hand: 3 × 10^7 times","section":"story"},{"source":"ref:bnid107902","machine":"myosin","label":"BNID 107902","section":"sources","href":"https://bionumbers.hms.harvard.edu/bionumber.aspx?id=107902"}]},{"id":"myosin-link-serca","machine":"myosin","kind":"qa","prompt":"Calcium switches myosin on. How does SERCA switch it off?","answer":"By pumping the calcium away.","explanation":"Calcium is the on switch for myosin, so removing it switches myosin off.","section":"story","topic":"purpose","sources":["link:serca"],"tags":["serca","calcium"],"difficulty":1,"url":"/machines/myosin#story","cites":[{"source":"link:serca","machine":"myosin","label":"Link to SERCA calcium pump","section":"story"}]},{"id":"myosin-kinesin-shared-core","machine":"myosin","kind":"qa","prompt":"Myosin and kinesin share almost no sequence identity. What do they share?","answer":"The same fold of the catalytic core.","explanation":"The two motor families probably evolved from a common ancestor; kinesin walks on microtubules, myosin on actin.","section":"story","topic":"purpose","sources":["evolution:Common core with kinesin","link:kinesin","ref:kull1996"],"tags":["kinesin","evolution"],"difficulty":2,"url":"/machines/myosin#story","cites":[{"source":"evolution:Common core with kinesin","machine":"myosin","label":"Common core with kinesin","section":"summary"},{"source":"link:kinesin","machine":"myosin","label":"Link to Kinesin","section":"story"},{"source":"ref:kull1996","machine":"myosin","label":"Kull et al.","section":"sources","anchor":"ref-kull1996","href":"https://doi.org/10.1038/380550a0"}]},{"id":"myosin-finer-method","machine":"myosin","kind":"qa","prompt":"How did Finer, Simmons and Spudich (1994) measure the step of a single myosin molecule?","answer":"With a laser trap holding one actin filament against a single myosin molecule.","explanation":"Each time the myosin bound, the filament jumped forward in a discrete step, averaging 11 nm at low load.","section":"evidence","topic":"numbers","sources":["evidence:finer1994-step","ref:finer1994"],"tags":["optical-trap","stroke"],"difficulty":2,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:finer1994-step","machine":"myosin","label":"Displacement produced by a single myosin molecule at low load (Finer JT 1994)","section":"evidence","anchor":"ev-finer1994-step"},{"source":"ref:finer1994","machine":"myosin","label":"Finer et al.","section":"sources","anchor":"ref-finer1994","href":"https://doi.org/10.1038/368113a0"}]},{"id":"myosin-stroke-dispute","machine":"myosin","kind":"qa","prompt":"Finer 1994 found a stroke of about 11 nm for muscle myosin. What stroke did Molloy 1995 find for a single head (S1)?","answer":"About 4 nm.","explanation":"The single-head estimate depends on how the broad spread of displacements is analysed, so the stroke size is disputed.","section":"evidence","topic":"debate","sources":["evidence:molloy1995-single-head-stroke","stat:Stroke per head, muscle myosin"],"tags":["stroke","disputed"],"difficulty":2,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:molloy1995-single-head-stroke","machine":"myosin","label":"Working stroke and force of a single myosin head (S1) (Molloy JE 1995)","section":"evidence","anchor":"ev-molloy1995-single-head-stroke"},{"source":"stat:Stroke per head, muscle myosin","machine":"myosin","label":"Key number: Stroke per head, muscle myosin","section":"summary"}]},{"id":"myosin-yildiz-hand-over-hand","machine":"myosin","kind":"qa","prompt":"Yildiz and colleagues tracked one dye on the lever of myosin-5. What step pattern showed that it walks hand over hand?","answer":"Long and short steps in turn (37 + 2x and 37 − 2x nm).","explanation":"If the same head always led, as in an inchworm, every step would be the same size. The centre of mass moves about 37 nm per ATP.","section":"evidence","topic":"numbers","sources":["evidence:yildiz2003-hand-over-hand","ref:yildiz2003"],"tags":["myosin-5","stepping"],"difficulty":3,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:yildiz2003-hand-over-hand","machine":"myosin","label":"Step size of a single dye on the myosin V light-chain domain (Yildiz A 2003)","section":"evidence","anchor":"ev-yildiz2003-hand-over-hand"},{"source":"ref:yildiz2003","machine":"myosin","label":"Yildiz et al.","section":"sources","anchor":"ref-yildiz2003","href":"https://doi.org/10.1126/science.1084398"}]},{"id":"myosin-uyeda-lever-test","machine":"myosin","kind":"qa","prompt":"What did Uyeda, Abramson and Spudich (1996) find when they changed the neck length of Dictyostelium myosin?","answer":"Gliding speed rose linearly with lever length.","explanation":"Speed fell on a line that reached zero near a fulcrum in the motor domain, so the neck acts as a lever arm.","section":"evidence","topic":"numbers","sources":["evidence:uyeda1996-velocity-vs-lever","stat:Velocity versus lever length","ref:uyeda1996"],"tags":["lever","motility"],"difficulty":2,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:uyeda1996-velocity-vs-lever","machine":"myosin","label":"Actin sliding velocity against lever-arm length (Uyeda TQ 1996)","section":"evidence","anchor":"ev-uyeda1996-velocity-vs-lever"},{"source":"stat:Velocity versus lever length","machine":"myosin","label":"Key number: Velocity versus lever length","section":"summary"},{"source":"ref:uyeda1996","machine":"myosin","label":"Uyeda et al.","section":"sources","anchor":"ref-uyeda1996","href":"https://doi.org/10.1073/pnas.93.9.4459"}]},{"id":"myosin-delacruz-method","machine":"myosin","kind":"qa","prompt":"How did De La Cruz and colleagues measure how much of the cycle a myosin-5 head stays strongly bound?","answer":"With pyrene-labelled actin, whose glow is quenched by strongly bound myosin, in stopped flow.","explanation":"Most heads stayed strongly bound for most of each cycle: a duty ratio of about 0.7.","section":"evidence","topic":"numbers","sources":["evidence:delacruz1999-duty-ratio","ref:delacruz1999"],"tags":["duty-ratio","stopped-flow"],"difficulty":3,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:delacruz1999-duty-ratio","machine":"myosin","label":"Fraction of single-headed myosin V strongly bound to actin during ATP turnover (De La Cruz EM 1999)","section":"evidence","anchor":"ev-delacruz1999-duty-ratio"},{"source":"ref:delacruz1999","machine":"myosin","label":"De La Cruz et al.","section":"sources","anchor":"ref-delacruz1999","href":"https://doi.org/10.1073/pnas.96.24.13726"}]},{"id":"myosin-rief-adp-gates","machine":"myosin","kind":"qa","prompt":"In single-molecule stepping of myosin-5 (Rief 2000), what showed that ADP release gates each step?","answer":"Adding ADP slowed the stepping rate, from 12.5 to 6.4 per second.","explanation":"The rate matches ADP release measured in solution by De La Cruz and colleagues.","section":"evidence","topic":"numbers","sources":["evidence:rief2000-dwell-rate","ref:rief2000"],"tags":["adp","optical-trap"],"difficulty":3,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:rief2000-dwell-rate","machine":"myosin","label":"Rate-limiting transition between myosin-V steps (Rief M 2000)","section":"evidence","anchor":"ev-rief2000-dwell-rate"},{"source":"ref:rief2000","machine":"myosin","label":"Rief et al.","section":"sources","anchor":"ref-rief2000","href":"https://doi.org/10.1073/pnas.97.17.9482"}]},{"id":"myosin-klebl-method","machine":"myosin","kind":"qa","prompt":"How did Klebl and colleagues (2025) see myosin-5 both before and after its stroke on actin?","answer":"They mixed myosin-ADP-Pi with actin and froze it 10 or 120 ms later (time-resolved cryo-EM).","explanation":"Primed motors fell from 62% at 10 ms to 36% at 120 ms, so both shapes could be compared on the same filament.","section":"evidence","topic":"numbers","sources":["evidence:lever-swing-klebl2025","ref:klebl2025"],"tags":["cryo-em","power-stroke"],"difficulty":2,"url":"/machines/myosin#evidence","cites":[{"source":"evidence:lever-swing-klebl2025","machine":"myosin","label":"Lever swing of myosin-5 on actin, primed to post-power stroke (Klebl DP 2025)","section":"evidence","anchor":"ev-lever-swing-klebl2025"},{"source":"ref:klebl2025","machine":"myosin","label":"Klebl et al.","section":"sources","anchor":"ref-klebl2025","href":"https://doi.org/10.1038/s41586-025-08876-5"}]}]}