Actin binding of a minispectrin.

Abstract A “minispectrin” has been constructed from the tail end of the α/β heterodimer, and its actin-binding properties have been characterised. It is a complex of the N-terminal fragment of the β-subunit consisting of the actin-binding domain plus the two first triple-helical repeats β1 and β2, and the C-terminal fragment of the α-subunit containing the repeats α19 and α20 plus the calmodulin-like domain. This minispectrin exists in a dimeric form that contains one copy of each polypeptide and binds to actin in a cooperative manner with an apparent K d of 2.5 μM. Calcium seems not to have any effect on its binding to actin. Electron microscopic analysis shows that the minispectrin decorates actin filaments as clusters, and induces formation of actin bundles. This study shows that the actin-binding region of the spectrin α/β heterodimer retains its functional properties in a truncated form and establishes basis for further research on spectrin's structure and function.