AN EPITOPE STRUCTURE FOR THE C-TERMINAL DOMAIN OF DYSTROPHIN AND UTROPHIN

The muscular dystrophy protein, dystrophin, and the closely related pr otein, utrophin, are large cytoskeletal proteins which link actin micr ofilaments to the plasma membrane. A panel of 38 monoclonal antibodies (mAbs) has been produced against the C-terminal domains of dystrophin and utrophin, This domain interacts with both dystrobrevins, via thei r ''leucine zipper'' coiled-coil helices, and syntrophins, adaptor pro teins which also interact with nitric oxide synthetase and transmembra ne sodium channels. The amino acid sequences recognized by the mAbs ha ve now been identified using a variety of epitope mapping techniques, including fragmentation by transposon mutagenesis, synthetic peptides, phage-displayed peptide libraries, and mutant dystrophins expressed i n transgenic mice. In addition to defining antibody recognition sites, mapping was sufficiently precise to provide structural information, s ince individual amino acids accessible on the surface of the native pr otein were identified in many cases. In two regions of the domain, sho rt linear epitopes were found in proline-rich sequences which may form surface loops, turns, or linkers, but these were separated by a third region which contained mainly conformational epitopes. The results ar e consistent with a loose and flexible structure for much of the C-ter minal domain, especially around the highly conserved second leucine zi pper or coiled-coil helix (CC-H2), but there is evidence for denaturat ion-resistant tertiary structure in the syntrophin-binding region and the first coiled-coil helix (CC-H1).