Smooth muscle α-actinin interaction with smitin
Actin–myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells also contain the actin filament-crosslinking protein α-actinin. In striated muscle sarcomeres, interactions between the myosin-binding protein titin and α-actinin in the Z-line provide an important structural linkage. We previously discovered a titin-like protein, smitin, associated with the contractile apparatus of smooth muscle cells. Purified native smooth muscle α-actinin binds with nanomolar affinity to smitin in smitin–myosin coassemblies in vitro. Smooth muscle α-actinin also interacts with striated muscle titin. In contrast to striated muscle α-actinin interaction with titin and smitin, which is significantly enhanced by PIP2, smooth muscle α-actinin interacts with smitin and titin equally well in the presence and absence of PIP2. Using expressed regions of smooth muscle α-actinin, we have demonstrated smitin-binding sites in the smooth muscle α-actinin R2–R3 spectrin-like repeat rod domain and a C-terminal domain formed by cryptic EF-hand structures. These smitin-binding sites are highly homologous to the titin-binding sites of striated muscle α-actinin. Our results suggest that direct interaction between α-actinin and titin or titin-like proteins is a common feature of actin–myosin II contractile structures in striated muscle and smooth muscle cells and that the molecular bases for α-actinin interaction with these proteins are similar, although regulation of these interactions may differ according to tissue.
smitin, titin, α-actinin, smooth muscle, PIP2
Chi, Richard J., Scott G. Olenych, Kyoungtae Kim, and Thomas CS Keller III. "Smooth muscle α-actinin interaction with smitin." The international journal of biochemistry & cell biology 37, no. 7 (2005): 1470-1482.
The international journal of biochemistry & cell biology