Smooth muscle α-actinin interaction with smitin

• Published in: The international journal of biochemistry & cell biology 2005-07, Vol.37 (7), p.1470-1482
• Main Authors: Chi, Richard J., Olenych, Scott G., Kim, Kyoungtae, Keller, Thomas C.S.
• Format: Article
• Language: English
• Subjects: Actinin - chemistry; Actinin - isolation & purification; Animals; Blotting, Far-Western; Chickens; Connectin; Muscle Proteins - chemistry; Muscle Proteins - isolation & purification; Muscle, Skeletal - chemistry; Muscle, Smooth - chemistry; PIP 2; Protein Binding; Protein Kinases - chemistry; Protein Kinases - isolation & purification; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Smitin; Smooth muscle; Titin; α-Actinin
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2005.02.014

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 PIP 2, smooth muscle α-actinin interacts with smitin and titin equally well in the presence and absence of PIP 2. 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.