Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Poster Abstracts

STRUCTURE OF PREPOWERSTROKE ACTOMYOSIN BY CRYOELECTRONMICROSCOPY AT 10 MS AND 5A Howard D White 1,2 ; Risi Cristina 1 ; David Klebl 2 ; Stephen Muench 2 ; Charlie Scarff 2 ; Vitold Galkin 1 ; 1 Eastern Virginia Medical Center, Physiological Sciences, Norfolk, VA, USA 2 Leeds University, Astbury Center, Leeds, United Kingdom We have determined the structure of the actomyosin complex formed 10 ms and 120 ms after mixing myosin-ADP-Pi with f-actin. High-resolution studies of actomyosin have been limited to equilibrium conditions with either ADP bound or an empty active site and the structure of the short lived primed, prepowerstroke, structure of the catalytic cycle has previously remained elusive. Here, using millisecond time-resolved cryo-electron microscopy we have determined the structure of the prepowerstroke actomyosin complex formed 10 ms after mixing myosin-ADP-Pi with f-actin. The predominant structure at 10 ms reveals myosin binding the actin filament through its lower 50 kDa subdomain with only the loop2 interacting with the actin surface. The predominant structure 120 ms after mixing with actin is a second conformational state in which the actin-binding cleft is closed and the lever is in a post-power stroke position, similar to previous strongly-bound actomyosin structures. Together, the two states represent the start and end positions of the powerstroke and allow us to assemble the most complete picture of the actomyosin catalytic cycle to date.

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