Key result
Cryo-electron tomography of porcine cardiac myofibrils revealed that alpha-actinin undergoes a ~21° contraction-induced swing motion along with a global twist in the actin lattice.
Why the study?
The 3D structure of the Z-disc has remained elusive due to the limited resolution of conventional electron microscopy.
Cryo-electron tomography of porcine cardiac myofibrils reveals that Z-disc integrity during contraction is maintained by structural flexibility within the actin-actinin complex.
Highlights Z-disc flexibility in contraction; extends sarcomere models but leaves open human translation.
The Z-disc forms a boundary between sarcomeres, which constitute structural and functional units of striated muscle tissue. Actin filaments from adjacent sarcomeres are cross-bridged by α-actinin in the Z-disc, allowing transmission of tension across the myofibril. Despite decades of studies, the 3D structure of Z-disc has been elusive due to the limited resolution of conventional electron microscopy. Here, we observed porcine cardiac myofibrils using cryo-electron tomography and reconstructed the 3D structures of the actinactinin cross-bridging complexes within the Z-discs in relaxed and activated states. We found that the α-actinin showed a contraction-induced swing motion along with a global twist in the actin lattice. Our observation suggests that the elasticity and the integrity of the Z-disc during the muscle contraction cycle are maintained by the structural flexibility within the actin-actinin complex.
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Oda et al. (2020) studied Normal cardiac muscle structure. Calcium and ATP (Ca+ATP) vs. EGTA and ATP (relaxed state) was evaluated on 3D structure of the actin-actinin cross-bridging complexes within the Z-discs. Cryo-electron tomography of porcine cardiac myofibrils revealed that alpha-actinin undergoes a ~21° contraction-induced swing motion along with a global twist in the actin lattice.