Characterization of actin and poly-L-proline binding sites of Acanthamoeba profilin with monoclonal antibodies and by mutagenesis.

We characterized several deletion and substitution mutations of Acanthamoeba profilin and nine monoclonal antibodies to Acanthamoeba profilin. The results provide two independent lines of evidence about the binding sites for actin and poly-L-proline on the profilin molecule. This new evidence is consistent with the main conclusions about these binding sites from previous structural and mutagenic studies. Mutagenesis also revealed that the native structure of profilin is very sensitive to substitutions and deletions at the C terminus. For example, profilin with a deletion of the eight C-terminal residues has many of the physical properties of a molten globule, yet remarkably still binds to actin. This instability may account for the lack of function of similar mutants in yeast.