The results of the current study indicate that the NNLS analysis in combination with biexponential curve fitting allows to correct for partial volume effects originating from blood flow in IVIM perfusion fraction measurements. Magn Reson Med 77:310-317, 2017. © 2016 Wiley Periodicals, Inc.

Dystrophin is essential to skeletal muscle function and confers resistance to the sarcolemma by interacting with cytoskeleton and membrane. In the present work, we characterized the behavior of dystrophin 11-15 (DYS R11-15), five spectrin-like repeats from the central domain of human dystrophin, with lipids. DYS R11-15 displays an amphiphilic character at the liquid/ air interface while maintaining its secondary ␣-helical structure. The interaction of DYS R11-15 with small unilamellar vesicles (SUVs) depends on the lipid nature, which is not the case with large unilamellar vesicles (LUVs). In addition, switching from anionic SUVs to anionic LUVs suggests the lipid packing as a crucial factor for the interaction of protein and lipid. The monolayer model and the modulation of surface pressure aim to mimic the muscle at work (i.e. dynamic changes of muscle membrane during contraction and relaxation) (high and low surface pressure). Strikingly, the lateral pressure modifies the protein organization. Increasing the lateral pressure leads the proteins to be organized in a regular network. Nevertheless, a different protein conformation after its binding to monolayer is revealed by trypsin proteolysis. Label-free quantification by nano-LC/ MS/MS allowed identification of the helices in repeats 12 and 13 involved in the interaction with anionic SUVs. These results, combined with our previous studies, indicate that DYS R11-15 constitutes the only part of dystrophin that interacts with anionic as well as zwitterionic lipids and adapts its interaction and organization depending on lipid packing and lipid nature. We provide strong experimental evidence for a physiological role of the central domain of dystrophin in sarcolemma scaffolding through modulation of lipid-protein interactions.Dystrophin is a rod-shaped cytoplasmic protein that constitutes a vital part of a protein complex that connects the cytoskeleton of muscle fibers to the surrounding extracellular matrix through the cell membrane. This long, filamentous protein (Fig. 1A) is essential to skeletal muscle function, which is demonstrated by the lethal pathophysiology associated with its deficiency, namely Duchenne muscular dystrophy (1). Several membrane and cytoskeletal binding partners of dystrophin have been identified, including ␤-dystroglycan from the dystrophin-glycoprotein complex (2, 3). ␤-Dystroglycan interacts with the cysteine-rich region of dystrophin that is located between the stabilizing central domain, which consists of 24 spectrin-like repeats and is known as the rod domain, and the C-terminal end of the molecule. Cytoskeletal actin interacts with the dystrophin molecule through two actin-binding domains, ABD1 and ABD2, which are situated at the N-terminal end and at the center of the dystrophin rod domain (repeats 11-15), respectively (4). The subsarcolemmal location of dystrophin and its association with both the cytoskeleton and membrane suggest a role in the mechanical regulation of membrane stress during contraction and elongation of muscle fi...