Phosphoinositides differentially regulate alpha-actinin flexibility and function.
Alpha-actinin is a cell-adhesion and cytoskeletal protein that bundles actin microfilaments and links these filaments directly to integrin-adhesion receptors. Phosphoinositides bind to and regulate the interaction of a-actinin with actin filaments and integrin receptors. In the present study, we demonstrate that PtdIns(3,4,5)P3 inhibits and disrupts a-actinin-bundling activity, whereas PtdIns(4,5)P2 can only inhibit activity. In addition, a protease-sensitivity assay was developed to examine the flexibility of the linker region between the actin-binding domain and the spectrin repeats of a-actinin. Both phosphoinositides influenced the extent of proteolysis and the cleavage sites. PtdIns(4,5)P2 binding decreased the proteolysis of a-actinin, suggesting a role in stabilizing the structure of the protein. In contrast, PtdIns(3,4,5)P3 binding enhanced a-actinin proteolysis, indicating an increase in the flexibility of the protein. Furthermore, phosphoinositide binding influenced the proteolysis of the N- and C-terminal domains of a-actinin, indicating regulation of structure within both domains. These results support the hypothesis that PtdIns(4,5)P2 and PtdIns(3,4,5)P3 differentially regulate a-actinin function by modulating the structure and flexibility of the protein.
Corgan
Anne Marie
AM
Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, USA.
Singleton
CoreyAyne
C
Santoso
Cynthia B
CB
Greenwood
Jeffrey A
JA
D008841:Actin Cytoskeleton / Q000378:metabolism; D000185:Actinin / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D000199:Actins / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000494:pharmacology*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D000199:Actins; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; C118303:phosphoinositide-3,4,5-triphosphate; D000185:Actinin