Orientation of the N-Terminal Lobe of the Myosin Regulatory Light Chain in Skeletal Muscle Fibers

Daniela Romano, Birgit D. Brandmeier, Yin-Biao Sun, David R. Trentham, Malcolm Irving

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The orientation of the N-terminal lobe of the myosin regulatory light chain (RLC) in demembranated fibers of rabbit psoas muscle was determined by polarized fluorescence. The native RLC was replaced by a smooth muscle RLC with a bifunctional rhodamine probe attached to its A, B, C, or D helix. Fiber fluorescence data were interpreted using the crystal structure of the head domain of chicken skeletal myosin in the nucleotide-free state. The peak angle between the lever axis of the myosin head and the fiber or actin filament axis was 100-110 degrees in relaxation, isometric contraction, and rigor. In each state the hook helix was at an angle of similar to 40 degrees to the lever/filament plane. The in situ orientation of the RLC D and E helices, and by implication of its N- and C-lobes, was similar in smooth and skeletal RLC isofornns. The angle between these two RLC lobes in rigor fibers was different from that in the crystal structure. These results extend previous crystallographic evidence for bending between the two lobes of the RLC to actin-attached myosin heads in muscle fibers, and suggest that such bending may have functional significance in contraction and regulation of vertebrate striated muscle.
Original languageEnglish
Pages (from-to)1418 - 1426
Number of pages9
JournalBiophysical Journal
Issue number6
Publication statusPublished - 21 Mar 2012


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