Phospholipids are new partners of dystrophin: modularity of the rod domain repeat binding to lipids.
Résumé
Dystrophin is a scaffolding protein of the skeletal muscle which is situated as the internal face of the muscle cell, lying along the sarcolemma. It is a 427 kDa protein made of several domains which anchored it at the sarcolemma via interaction of the CYS-rich domain with intrinsic proteins and at the cytoskeleton via interaction of the N-terminal end and several repeats of the central rod domain with F-actin. Here we report for the interaction of the central rod domain with the membrane phospholipids. The huge of the molecule, the central rod domain, is constituted by 24 spectrin-like repeats which places dystrophin in the spectrin super family of proteins. However, the striking difference of dystrophin among this large family is that first, it does not forms dimers and second, that the repeats are not as homologous between them as for the other members of the family. In particular, they have not a definite length in terms in residue number per repeat and they do not align as well as for the Α- and Α-spectrins. In addition, they are separated in three sub-domains by four hinges. In a first work, we studied the lipid binding properties of the 2nd repeat and showed that this repeat binds to lipids by electrostatic as well as hydrophobic interactions with anionic lipids. We show that this is a unique property of the first N-terminal domain constituted of the repeats 1-3 situated between hinges 1 and 2 compared to the other sub-domain constituted by the repeats 20-24 situated between hinges 3 and 4. This lipid binding property is accompanied by a relative instability of R1-3 compared toR20-24 and a faster refolding velocity capability. Increasing the knowledge to the central part of the rod domain, we show now that all the repeats 4-19 are able to bind to lipids. First experiments about transconformation of the repeats upon binding to lipids demonstrate that the coiled-coil 3D structure of the repeats opens, decreasing the inter-helical interactions while allowing interactions of the Α-helices with lipids. Our results demonstrate that the dystrophin repeats are not interchangeable and give attempts to understand the rescue scores observed in mdx dystrophin deficient mouse transformed with mini- or micro-dystrophin constructs containing only few specific repeats. [1] E. Le Rumeur, Y. Fichou, S. Pottier, C. Mouro-Rondeau, F. Gaboriau, J. Gallay, M. Vincent, A. Bondon, Interaction of dystrophin rod domain with membrane phospholipids. Evidence of a close proximity between tryptophan residues and lipids, J Biol Chem 278 (2003) 5993-6001. [2] E. Le Rumeur, S. Pottier, G. Da Costa, L. Metzinger, L. Mouret, C. Rocher, M. Fourage, C. Rondeau-Mouro, A. Bondon, Binding of the dystrophin second repeat to membrane phospholipids is dependent upon lipid packing, Biochim Biophys Acta, Biomembranes 1768 (2007) 648-654. [3] S. Legardinier, J.-F. Hubert, O. Le Bihan, C. Tascon, C. Rocher, C. Raguénès-Nicol, A. Bondon, S. Hardy, E. Le Rumeur, Sub-domains of the dystrophin rod domain display contrasting lipid-binding and stability properties, Biochim Biophys Acta, Proteins and Proteomics 1784 (2008) 672-682.