DIRECT VISUALIZATION OF COLLAGEN-BOUND PROTEOGLYCANS BY TAPPING-MODE ATOMIC-FORCE MICROSCOPY

Most studies on the interaction of collagen with proteoglycans, two un iversal components of connective tissues, use technical approaches whi ch substantially modify the shape and size of the proteoglycans themse lves, In the present study unfixed, untreated collagen fibrils from ra t tail tendon were dehydrated and observed by tapping-mode atomic forc e microscopy. The surface of collagen fibrils immediately reveals a pe riodic alternation of gap and overlap zones. A thin, transverse ridge decorates the gap zone, while other filamentous structures run on the fibril surface, either parallel or perpendicular to the fibril axis. T hese surface structures are much enhanced by Cupromeronic Blue preincu bation, while pretreatment with chondroitinase ABC removes them comple tely, leaving barely detectable transverse ridges. The ridge and filam ents are likely to represent, respectively, the core protein and the g lycosaminoglycan side chains of proteoglycans, displayed with a far be tter resolution than with conventional histochemical or immunohistoche mical techniques. Our data suggest that proteoglycan molecules are cap able of different, multiple interactions with the collagen fibril surf ace as well as with each other. (C) 1997 Academic Press.