CRYSTAL PACKING INDUCES A CONFORMATIONAL CHANGE IN PROFILIN-I FROM ACANTHAMOEBA-CASTELLANII

Profilin-I from Acanthamoeba castellanii is a 13-kDa protein that bind s actin and poly-L-proline. The native protein has been crystallized i n two different but closely related forms. The second form proved more amenable to three-dimensional structural determination using heavy-at om isomorphous methods to obtain crystallographic phase information. W e used the second crystal structure as a test molecule in the molecula r replacement procedure to determine the structure of the first crysta l form of profilin-I. More residues participate in crystal lattice con tacts in the first crystal form than in the second. The two crystal fo rms differ significantly in the C-terminal helix that interacts with a ctin and in the loop preceding this helix. Coordinates of some main ch ain atoms here differ by about 1.0 Angstrom and side chain atoms diffe r by more than 2.0 Angstrom. (C) 1998 Academic Press.