Mutations in dystrophin trigger muscular dystrophy, however its structure-function relationship is less understood. Dystrophin interacts with F-actin using its N-terminal actin binding domain (N-ABD), which is a tandem repeat of calponin-homology (CH) domains. Previous X-ray structure indicated that the N-ABD is a domain-swapped dimer, with each monomer in an 'open' conformation in which the two CH domains do not interact. Here we investigated the conformation of dystrophin N-ABD in solution using pyrene excimer fluorescence. Pyrene-labeled single cysteine mutants did not show excimer fluorescence indicating the absence of either parallel or anti-parallel dimers. Pyrene-labeled wild-type protein showed excimer fluorescence indicating that the two native cysteines are close in space which is only possible if dystrophin N-ABD exists in a 'closed' conformation with significant interactions between the two CH domains. Upon binding to F-actin, excimer fluorescence increased indicating that this domain transitions to a more compact closed conformation. This study demonstrates for the first time the conformational transition of a dystrophin domain during its function, and suggests that such structural dynamics might play an important role in controlling dystrophin function.

Conformational dynamics of the N-terminal actin binding domain of dystrophin probed using pyrene excimer fluorescence

243rd National Meeting (2012)

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