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          Institute: MPI für medizinische Forschung     Collection: Abteilung Biophysik     Display Documents

ID: 23080.0, MPI für medizinische Forschung / Abteilung Biophysik
Structural Features of Cross-Bridges in Isometrically Contracting Skeletal Muscle
Translation of Title:Structural Features of Cross-Bridges in Isometrically Contracting Skeletal Muscle
Authors:Kraft, Theresia; Mattei, Thomas; Radocaj, Ante; Piep, Birgit; Nocula, Christoph; Furch, Marcus; Brenner, Bernhard
Date of Publication (YYYY-MM-DD):2002-05
Title of Journal:Biophysical Journal
Journal Abbrev.:Biophys. J.
Issue / Number:5
Start Page:2536
End Page:2547
Copyright:© 2002 by the Biophysical Society
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:Two-dimensional x-ray diffraction was used to investigate structural features of cross-bridges that generate force in isometrically contracting skeletal muscle. Diffraction patterns were recorded from arrays of single, chemically skinned rabbit psoas muscle fibers during isometric force generation, under relaxation, and in rigor. In isometric contraction, a rather prominent intensification of the actin layer lines at 5.9 and 5.1 nm and of the first actin layer line at 37 nm was found compared with those under relaxing conditions. Surprisingly, during isometric contraction, the intensity profile of the 5.9-nm actin layer line was shifted toward the meridian, but the resulting intensity profile was different from that observed in rigor. We particularly addressed the question whether the differences seen between rigor and active contraction might be due to a rigor-like configuration of both myosin heads in the absence of nucleotide (rigor), whereas during active contraction only one head of each myosin molecule is in a rigor-like configuration and the second head is weakly bound. To investigate this question, we created different mixtures of weak binding myosin heads and rigor-like actomyosin complexes by titrating MgATP S at saturating [Ca2+] into arrays of single muscle fibers. The resulting diffraction patterns were different in several respects from patterns recorded under isometric contraction, particularly in the intensity distribution along the 5.9-nm actin layer line. This result indicates that cross-bridges present during isometric force generation are not simply a mixture of weakly bound and single-headed rigor-like complexes but are rather distinctly different from the rigor-like cross-bridge. Experiments with myosin-S1 and truncated S1 (motor domain) support the idea that for a force generating cross-bridge, disorder due to elastic distortion might involve a larger part of the myosin head than for a nucleotide free, rigor cross-bridge.
Comment of the Author/Creator:The authors would like to thank S. Xu, D. Gilroy, G. Melvin, and L. C. Yu (National Institutes of Health, NIAMS, Bethesda, MD), S. Slawson (SRS Daresbury, United Kingdom), G. Rapp (EMBL-outstation, DESY, Hamburg, Germany), as well as T. Scholz, B. Heins-Höntsch, and M. Hoppe (Medical School Hannover, Germany) for their contribution to this work. The work was supported by the EU "Access to large facilities"-program and by the Deutsche Forschungsgemeinschaft (Br849/12-1).
External Publication Status:published
Document Type:Article
Communicated by:Wulf Kaiser
Affiliations:MPI für medizinische Forschung/Abteilung Biophysik
External Affiliations:Molecular and Cellular Physiology, Medical School, D-30625 Hannover, Germany
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