TY - JOUR

T1 - X-ray recordings reveal how a human disease-linked skeletal muscle α-actin mutation leads to contractile dysfunction

AU - Ochala, Julien

AU - Ravenscroft, Gianina

AU - McNamara, Elyshia

AU - Nowak, Kristen J.

AU - Iwamoto, Hiroyuki

PY - 2015/12

Y1 - 2015/12

N2 - In humans, mutant skeletal muscle α-actin proteins are associated with contractile dysfunction, skeletal muscle weakness and a wide range of primarily skeletal muscle diseases. Despite this knowledge, the exact molecular mechanisms triggering the contractile dysfunction remain unknown. Here, we aimed to unravel these. Hence, we used a transgenic mouse model expressing a well-described D286G mutant skeletal muscle α-actin protein and recapitulating the human condition of contractile deregulation and severe skeletal muscle weakness. We then recorded and analyzed the small-angle X-ray diffraction patterns of isolated membrane-permeabilized myofibers. Results showed that upon addition of Ca2+, the intensity changes of the second (1/19nm-1) and sixth (1/5.9nm-1) actin layer lines and of the first myosin meridional reflection (1/14.3nm-1) were disrupted when the thin-thick filament overlap was optimal (sarcomere length of 2.5-2.6μm). However these reflections were normal when the thin and thick filaments were not interacting (sarcomere length>3.6μm). These findings demonstrate, for the first time, that the replacement of just one amino acid in the skeletal muscle α-actin protein partly prevents actin conformational changes during activation, disrupting the strong binding of myosin molecules. This leads to a limited myosin-related tropomyosin movement over the thin filaments, further affecting the amount of cross-bridges, explaining the contractile dysfunction.

AB - In humans, mutant skeletal muscle α-actin proteins are associated with contractile dysfunction, skeletal muscle weakness and a wide range of primarily skeletal muscle diseases. Despite this knowledge, the exact molecular mechanisms triggering the contractile dysfunction remain unknown. Here, we aimed to unravel these. Hence, we used a transgenic mouse model expressing a well-described D286G mutant skeletal muscle α-actin protein and recapitulating the human condition of contractile deregulation and severe skeletal muscle weakness. We then recorded and analyzed the small-angle X-ray diffraction patterns of isolated membrane-permeabilized myofibers. Results showed that upon addition of Ca2+, the intensity changes of the second (1/19nm-1) and sixth (1/5.9nm-1) actin layer lines and of the first myosin meridional reflection (1/14.3nm-1) were disrupted when the thin-thick filament overlap was optimal (sarcomere length of 2.5-2.6μm). However these reflections were normal when the thin and thick filaments were not interacting (sarcomere length>3.6μm). These findings demonstrate, for the first time, that the replacement of just one amino acid in the skeletal muscle α-actin protein partly prevents actin conformational changes during activation, disrupting the strong binding of myosin molecules. This leads to a limited myosin-related tropomyosin movement over the thin filaments, further affecting the amount of cross-bridges, explaining the contractile dysfunction.

KW - Actin

KW - Muscle disease

KW - Myosin

KW - Small-angle X-ray scattering

UR - http://www.scopus.com/inward/record.url?scp=84947046685&partnerID=8YFLogxK

U2 - 10.1016/j.jsb.2015.09.008

DO - 10.1016/j.jsb.2015.09.008

M3 - Journal article

C2 - 26407659

AN - SCOPUS:84947046685

VL - 192

SP - 331

EP - 335

JO - Journal of Structural Biology

JF - Journal of Structural Biology

SN - 1047-8477

IS - 3

ER -