Structure of the Split PH domain and Distinct Lipid Binding Properties of the PH‐PDZ Supramodule of α‐Syntrophin

Objective To solve the structure of PH N ‐PDZ‐PH C tandem in the alpha‐syntrophin and uncover the distinct lipid binding properties of the supramodule. Methods We combined biochemistry, NMR and molecular biology approach. Results We solved the solution structure of the PH N ‐PDZ‐PH C tandem of α‐syntrophin. The split PH domain of α‐syntrophin adopts a canonical, intra‐molecular PH domain fold. We further showed that the isolated partial PH domains of α‐syntrophin (PH N and PH C ), although completely unfolded, remain soluble in solution. Mixing of the two isolated domains induces de novo folding and yields a stable PH domain. Our results demonstrate that two complementary partial PH domains are capable of binding to each other, either intra‐ or inter‐molecularly, to form an intact PH domain. We further showed that the PH N ‐PDZ‐PH C tandem forms a functional distinct supramodule, in which the split PH domain and the PDZ domain function synergistically in binding to inositol phospholipids. Conclusion The split PH domain adopts an intra‐molecular PH domain folding. And the split PH domain and the PDZ domain function synergistically in binding to inositol phospholipids. This work was supported by grants from the Research Grants Council of Hong Kong, and the Human Frontier Science Program to M.Z and from NIH to S.C.F. M.Z. was a recipient of the Croucher Foundation Senior Research Fellow award.