title: Smooth muscle alpha-actinin interaction with smitin.
abstract: Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells also contain the actin filament-crosslinking protein alpha-actinin. In striated muscle sarcomeres, interactions between the myosin-binding protein titin and alpha-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 alpha-actinin binds with nanomolar affinity to smitin in smitin-myosin coassemblies in vitro. Smooth muscle alpha-actinin also interacts with striated muscle titin. In contrast to striated muscle alpha-actinin interaction with titin and smitin, which is significantly enhanced by PIP2, smooth muscle alpha-actinin interacts with smitin and titin equally well in the presence and absence of PIP2. Using expressed regions of smooth muscle alpha-actinin, we have demonstrated smitin-binding sites in the smooth muscle alpha-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 alpha-actinin. Our results suggest that direct interaction between alpha-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 alpha-actinin interaction with these proteins are similar, although regulation of these interactions may differ according to tissue.
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Chi
authors.forename: Scott G
authors.initials: SG
authors.lastname: Olenych
authors.forename: Kyoungtae
authors.initials: K
authors.lastname: Kim
authors.forename: Thomas C S
authors.initials: TC
authors.lastname: Keller
mesh_terms: D000185:Actinin / Q000737:chemistry* / Q000302:isolation & purification; D000818:Animals; D026481:Blotting, Far-Western; D002645:Chickens; D064211:Connectin; D009124:Muscle Proteins / Q000737:chemistry* / Q000302:isolation & purification; D018482:Muscle, Skeletal / Q000737:chemistry; D009130:Muscle, Smooth / Q000737:chemistry*; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry* / Q000302:isolation & purification; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; D000185:Actinin; D011494:Protein Kinases