2W4W

Isometrically contracting insect asynchronous flight muscle quick frozen after a quick stretch step

Summary for 2W4W

• Entry DOI: 10.2210/pdb2w4w/pdb
• Related: 1B7T 1DFK 1DFL 1KK7 1KK8 1KQM 1KWO 1L2O 1QVI 1S5G 1SCM 1SR6 1WDC 2W4T
• EMDB information: 1584 1585
• Descriptor: MYOSIN HEAVY CHAIN, STRIATED MUSCLE, MYOSIN REGULATORY LIGHT CHAIN, STRIATED ADDUCTOR MUSCLE, MYOSIN ESSENTIAL LIGHT CHAIN, STRIATED ADDUCTOR MUSCLE (3 entities in total)
• Functional Keywords: contractile protein, methylation, atp-binding, isometric contraction, microtomy, freeze substitution, muscle protein, calmodulin-binding, motor protein, actin-binding
• Biological source: ARGOPECTEN IRRADIANS (BAY SCALLOP); More
• Total number of polymer chains: 3
• Total formula weight: 127471.49

Authors

Wu, S.,Liu, J.,Reedy, M.C.,Tregear, R.T.,Winkler, H.,Franzini-Armstrong, C.,Sasaki, H.,Lucaveche, C.,Goldman, Y.E.,Reedy, M.K.,Taylor, K.A. (deposition date: 2008-12-02, release date: 2010-08-25, Last modification date: 2024-05-08)

Primary citation

Wu, S.,Liu, J.,Reedy, M.C.,Perz-Edwards, R.J.,Tregear, R.T.,Winkler, H.,Franzini-Armstrong, C.,Sasaki, H.,Lucaveche, C.,Goldman, Y.E.,Reedy, M.K.,Taylor, K.A.
Structural Changes in Isometrically Contracting Insect Flight Muscle Trapped Following a Mechanical Perturbation.
Plos One, 7:39422-, 2012

PubMed Abstract: The application of rapidly applied length steps to actively contracting muscle is a classic method for synchronizing the response of myosin cross-bridges so that the average response of the ensemble can be measured. Alternatively, electron tomography (ET) is a technique that can report the structure of the individual members of the ensemble. We probed the structure of active myosin motors (cross-bridges) by applying 0.5% changes in length (either a stretch or a release) within 2 ms to isometrically contracting insect flight muscle (IFM) fibers followed after 5-6 ms by rapid freezing against a liquid helium cooled copper mirror. ET of freeze-substituted fibers, embedded and thin-sectioned, provides 3-D cross-bridge images, sorted by multivariate data analysis into ~40 classes, distinct in average structure, population size and lattice distribution. Individual actin subunits are resolved facilitating quasi-atomic modeling of each class average to determine its binding strength (weak or strong) to actin. ~98% of strong-binding acto-myosin attachments present after a length perturbation are confined to "target zones" of only two actin subunits located exactly midway between successive troponin complexes along each long-pitch helical repeat of actin. Significant changes in the types, distribution and structure of actin-myosin attachments occurred in a manner consistent with the mechanical transients. Most dramatic is near disappearance, after either length perturbation, of a class of weak-binding cross-bridges, attached within the target zone, that are highly likely to be precursors of strong-binding cross-bridges. These weak-binding cross-bridges were originally observed in isometrically contracting IFM. Their disappearance following a quick stretch or release can be explained by a recent kinetic model for muscle contraction, as behaviour consistent with their identification as precursors of strong-binding cross-bridges. The results provide a detailed model for contraction in IFM that may be applicable to contraction in other types of muscle.

PubMed: 22761792
DOI: 10.1371/JOURNAL.PONE.0039422

Experimental method

ELECTRON MICROSCOPY (35 Å)