Contractile proteins

Myocytes are a key cell type that enable animal movement, but their evolutionary origins remain unclear. Colgren and Nichols describe molecular and functional similarities between a contractile module in tissues of a sponge and muscle tissues in other animals, indicating a common evolutionary origin.

Heart muscle cells are inactivated when they shorten during ejection, accelerating relaxation to facilitate refilling before the next beat. The authors propose that sequential folding of myosin motors onto the filament backbone may be responsible for shortening-induced de-activation in the heart.

The structure of myosin-2 in the shutdown state reveals how the shutdown state is stabilized and how phosphorylation of light chains allows myosin to be activated.

Titin determines the elasticity of the sarcomere and integrates into both the Z-disc and the M-band. Here, the authors generate a BioID mouse to study the titin interactome at the Z-disc region in neonatal and adult heart and skeletal muscle.

Titin regulates myocyte stiffness through uncoiling and unfolding but these two processes cannot fully explain its elasticity. Here, the authors use atomic force microscopy to study the properties of titin disulfide bonds, showing that disulfide isomerization represents a third mode of titin elasticity.