Actophorin (ADF/cofilin)

(See ADF/Cofilin Pages)

One of the earliest member of the ADF/cofilin family to be identified (Cooper et al, 1986), later sequence analysis (Quirk et al, 1993) confirmed that actophorin is a member. Actophorin is not pH sensitive in the way that  vertebrate ADF and Cofilin is (Maciver et al, 1998).   Actophorin binds F-actin as the ADF/cofilins do at pH 6.5, but at all values of pH tested through 6.6-8.5. Actophorin binding to F-actin is not sensitive to calcium, but is inhibited by inorganic phosphate, tropomyosin and phalloidin (Maciver et al, 1991).  Actophorin interacts more strongly with actin with bound ADP than with ATP bound (Maciver & Weeds, 1994).   Severing by actophorin is dependent on the filament length, longer filaments being more rapidly severed.  Like other ADF/cofilins actophorin is phosphorylated blocking actin binding but does not change the structure of actophorin detectibly (Blanchoin et al, 2000).

References:-

Cooper, J. A., Blum, J.D ., Williams, R.C. Jr and Pollard, T.D. (1986). "Purification and Characterization of Actophorin, a New 15,000-Dalton Actin-binding Protein from Acanthamoeba castellanii." J. Biol. Chem. 261(1), 477-485.

Maciver, S. K., Zot,   H.G.and Pollard, T.D. (1991a). "Characterization of actin filament severing by actophorin from Acanthamoeba castellanii." J. Cell Biol. 115, 1611-1620.

Maciver, S. K.,Wachsstock, D.H., Schwarz, S.H., Pollard, T.D.(1991b). "The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha actinin." J. Cell Biol. 115, 1621-1628.

Maciver, S. K. & Weeds, A.G.  (1994). "Actophorin preferentially binds monomeric ADP-actin over ATP-bound actin: consequences for cell locomotion." FEBS Letters 347, 251-256.

Quirk, S., Maciver, S.K. , Ampe, C., Doberstein, S.K., Kaiser, D.A., VanDamme, J., Vandekerckhove, J.S., and Pollard, T.D.(1993). "Primary structure of and studies on Acanthamoeba actophorin." Biochemistry 32, 8525-8533.