SECONDARY STRUCTURE AND TOPOLOGY OF ACANTHAMOEBA PROFILIN-I AS DETERMINED BY HETERONUCLEAR NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The protein profilin binds to both actin and the head groups of poly(p hosphoinositide)s and may regulate both actin assembly and the phospho inositide signaling pathway. As a first step in understanding the acti vity of profilin at the molecular level, we have determined the second ary structure of Acanthamoeba profilin I in solution using multidimens ional, heteronuclear NMR spectroscopy. Using a combination of triple-r esonance (H-1, C-13, N-15) experiments, we obtained virtually complete backbone and side-chain resonance assignments based solely on scalar couplings. 3D and 4D NOESY experiments were then used to determine the secondary structure and global fold of Acanthamoeba profilin I. The c entral feature of the protein structure is a five-stranded antiparalle l beta-sheet flanked by three helices and a short two-stranded antipar allel beta-sheet.