The major proteoglycan of adult rabbit skeletal muscle. Relationship to small proteoglycans of other tissues

We have been interested in examining the putative biological role(s) of the major proteoglycan of adult skeletal muscle. The small proteoglycans of adult rabbit skeletal muscle and tendon were extracted and purified by sequential density-gradient ultracentrifugation, ion-exchange chromatography and gel filtration. They appeared to be homogeneous by the criterion of gel electrophoresis in SDS and to yield one major product, the core protein, after digestion with chondroitin ABC lyase, also observed after gel electrophoresis. Two major products were obtained when the intact proteoglycans were cleaved by CNBr, and those peptides were separated by SDS/PAGE and by ion-exchange chromatography. Sequencing of the N-terminal amino acids of either the intact proteoglycans or the CNBr-cleaved products allowed for comparison of the muscle and tendon proteoglycan with derived amino acid sequences previously reported for bovine bone proteoglycan. The bone and tendon proteoglycan sequences were remarkably similar, whereas those of the muscle proteoglycan differed from the other two molecules. The major site of glycosaminoglycan substitution was on a peptide fragment distant from the N-terminus, and a presumptive serine residue at position 4 from the N-terminus also appeared to be substituted, perhaps with a small glycosaminoglycan chain. These results provide some insight into the diversity of small proteoglycans of the PG-II class and provide a basis for exploring their mode of genetic expression.