Shared and distinct structural features of interstitial proteoglycans from different bovine tissues revealed by electron microscopy

Large and small interstitial proteoglycans were purified from different bovine tissues, i.e. cartilage, sclera, tendon, aorta, cornea, and bone. The structure of the molecules was compared using the glycerol spraying/rotary shadowing technique for electron microscopy. Large proteoglycans from sclera and tendon have a core protein with a domain structure similar to that previously reported for cartilage proteoglycans (Paulsson, M., M?rgelin, M., Wiedemann, H., Beardmore-Gray, M., Dunham, D., Hardingham, T., Heineg?rd, D., Timpl, R., and Engel, J. (1987) Biochem. J. 245, 763-772). It is comprised of a pair of globules at one end of the molecule, connected by a short extended segment, followed by a long extended domain which is terminated by a third globular domain. Large aorta proteoglycans show a somewhat different structure, with only one globular domain at each end of a long extended segment. Large sclera and aorta proteoglycans form aggregates with hyaluronate and cartilage link protein in a manner similar to that of large cartilage proteoglycans. The large proteoglycans show considerable tissue variability with regard to number, length, and spacing of glycosaminoglycan side chains. The small proteoglycans reveal a small globular core protein to which one or two glycosaminoglycans are attached. Although the main structural features do not differ, proteoglycans of the S1 class have an average glycosylation close to two glycosaminoglycans/molecule, while that of the S2 class is close to one. Differences in glycosaminoglycan length were observed between tissues and between the S1 and S2 class of proteoglycan derived from a single tissue.