PHYSICAL-PROPERTIES OF DYSTROPHIN ROD DOMAIN

We have prepared two fragments of the human dystrophin rod domain, eac h containing eight spectrin-like repeating units, by expression in Esc herichia coli. The first corresponds to the central portion of the rod , the other to three repeats from the N-terminal end, fused to five re peats from the C-terminal end. The latter makes up the entire mutant r od, found in a patient with mild (Becker-type) muscular dystrophy. Bot h fragments were found to possess an ordered, stable structure, and ha d the form of short rod-like particles in the electron microscope. Mol ecular weight determinations by sedimentation equilibrium revealed tha t both polypeptides were monomeric in solution, suggesting that the dy strophin rod domain is incapable of forming an antiparallel homodimer. This supports the inference from sequence analyses [Winder et al., 19 95: FEES Lett. 369:27-33, 1996: Biochem. Sec. Trans. 24:2805] that the dystrophin rod domain lacks the arrangement of sites required for lat eral self-association, and that dystrophin, unlike the other known pro teins of the spectrin superfamily, may thus exist as a monomer. (C) 19 97 Wiley-Liss, Inc.