3-DIMENSIONAL SOLUTION STRUCTURE OF ACANTHAMOEBA PROFILIN-I

We have determined a medium resolution three-dimensional solution stru cture of Acanthamoeba profilin-I by multidimensional nuclear magnetic resonance spectroscopy. This 13-kD actin binding protein consists of a five stranded antiparallel beta sheet flanked by NH2- and COOH-termin al helices on one face and by a third helix and a two stranded beta sh eet on the other face. Data from actin-profilin cross-linking experime nts and the localization of conserved residues between profilins in di fferent phyla indicate that actin binding occurs on the molecular face occupied by the terminal helices. The other face of the molecule cont ains the residues that differ between Acanthamoeba profilins-I and II and may be important in determining the difference in polyphosphoinosi tide binding between these isoforms. This suggests that lipids and act in bind to different faces of the molecule.