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).
Blanchoin, L. & Pollard, T. D. (1998).
"Interaction of actin monomers with Acanthamoeba actophorin
(ADF/cofilin) and profilin." J.Biol.Chem. 273, 25106-25111.
Blanchoin, L. & Pollard, T. D. (1999).
"Mechanism of interaction of Acanthamoeba actophorin (ADF/cofilin)
with actin filaments." J.Biol.Chem. 274(22), 15538-15546.
Blanchoin, L., Robinson, R.C., (2000). "Phosphorylation
of Acanthamoeba actophorin (ADF/cofilin) blocks interaction with actin
without a change in atomic structure." J.Mol.Biol. 295,
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,
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.