The atomic structure of human dystrophin spectrin-like repeat 24.

The structure of spectrin-like repeat 24 of human dystrophin was determined at 2.5 Å effective resolution. The structure exhibits a three-helix bundle fold, common to all spectrin-repeat family members, and shares a high degree of homology with existing structures of spectrin-like repeat 1 from dystrophin and utrophin. The structure provides molecular details of the atomic interactions that stabilize the repeat, including hydrophobic interactions and inter-helix and intra-helix salt bridges. AlphaFold models of the repeat are in excellent agreement with the structure, showing an all-atom r.m.s.d. of 1.13 Å. Accurate modeling of SR24 supports AlphaFold modeling of all 24 of the dystrophin spectrin-like repeats and the use of these models in predicting the molecular determinants of dystrophin stability, a key aspect of its biological function as a structural protein that cross-links actin filaments to the dystrophin-glycoprotein complex to mediate a mechanical connection between the cytoskeleton and the extracellular matrix.