THE SOLUTION STRUCTURE OF THE PLECKSTRIN-HOMOLOGY-DOMAIN OF MOUSE-SON-OF-SEVENLESS-1 (MSOS1)

The solution structure of the pleckstrin homology CPH) domain of mouse Son-of-sevenless 1 (mSos1), a guanine nucleotide exchange factor for Ras, was determined by multidimensional NMR spectroscopy. The structur e of the mSos1 PH domain involves the fundamental PH fold, consisting of seven beta-strands and one alpha-helix at the C terminus, as determ ined for the PH domains of other proteins. By contrast, the mSos1 PH d omain showed two major characteristic features. First, the N-terminal region, whose amino acid sequence is highly conserved among Sos protei ns, was found to form an cc-helix, which interacts with the beta-sheet structure of the fundamental PH fold. Second, there is a long unstruc tured loop between beta 3 and beta 4. Furthermore, the mSos1 PH domain was found to bind phosphatidylinositol-4,5-bisphosphate by a centrifu gation assay. The addition of inositol-1,4,5-trisphosphate to the mSos 1 PH domain induced backbone amide chemical shift changes mainly in th e beta 1/beta 2 loop and the N- and C-terminal parts of the long beta 3/beta 4 loop. This inositol-1,4,5-trisphosphate-binding mode of the m Sos1 PH domain is somewhat similar to those of the PH domains of pleck strin and phospholipase C delta(1), and is clearly different from thos e of other PH domains. (C) 1997 Academic Press Limited.