Molecular cloning of chicken myosin-binding protein (MyBP) H (86-kDa protein) reveals extensive homology with MyBP-C (C-protein) with conserved immunoglobulin C2 and fibronectin type III motifs.

The complete nucleotide sequence of a cDNA clone encoding the chicken skeletal muscle myosin-binding protein H (MyBP-H), formerly termed 86-kDa protein, has been established and the predicted amino acid sequence compared with other proteins entered into the GenBank data base. The full-length cDNA of 2066 base pairs contains a single open reading frame of 1611 base pairs encoding a muscle-specific protein of 58,487 Da. The predicted molecular weight differs significantly from the relative mobility of 86-kDa protein in reducing sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE). The full-length protein expressed in Escherichia coli also exhibits an anomalously slow mobility in SDS-PAGE; this gel retardation is a property of the N-terminal 24 kDa of the protein which contain two extended motifs of alternating alanine and proline residues, resembling the N terminus of skeletal muscle myosin light chain 1 (Nabeshima, Y. I., Fujii-Kuriyama, Y., Muramatsu, M., and Ogata, K. (1984) Nature 308, 333-338). The C-terminal 40 kDa share 49.6% sequence identity and 17% conservative substitutions with chicken skeletal muscle MyBP-C (C-protein) (Einheber, S., and Fischman, D. A. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 2157-2161). The protein contains four internal repeats of approximately 100 amino acids each, two of which bear significant resemblance to the C2 set of the immunoglobulin superfamily, and the other two are related to the type III fibronectin repeat. The arrangement of these repeats, -III-C2-III-C2-, is identical to that seen in the C-terminal 40-kDa section of MyBP-C. This repeat structure is implicated in myosin binding for the MyBP family. Finally, genomic Southern blots indicate that a single gene encodes fast skeletal muscle MyBP-H.