The solution structure of the pleckstrin homology domain of mouse Son-of-sevenless 1 (mSos1)

The solution structure of the plecktrin homology (PH) domain of mouse Son-of-sevenless 1 (mSos1), a guanine nucleotide exchange factor for Ras, was determined by multidimensional NMR spectroscopy. The structure of the mSos1 PH domain involves the fundamental PH fold, consisting of seven β-strands and one α-helix at the C terminus, as determined for the PH domains of other proteins. By contrast, the mSos1 PH domain showed two major characteristic features. First, the N-terminal region, whose amino acid sequence is highly conserved among Sos proteins, was found to form an α-helix, which interacts with the β-sheet structure of the fundamental PH fold. Second, there is a long unstructured loop between β3 and β4. Furthermore, the mSos1 PH domain was found to bind phosphatidylinositol-4,5-bisphosphate by a centrifugation assay. The addition of inositol-1,4,5-trisphosphate to the mSos1 PH domain induced backbone amide chemical shift changes mainly in the β1/β2 loop and the N- and C-terminal parts of the long β3/β4 loop. This inositol-1,4,5-trisphosphate-binding mode of the mSos1 PH domain is somewhat similar to those of the PH domains of pleckstrin and phospholipase Cδ₁, and is clearly different from those of other PH domains.