Hierarchical assembly and the onset of banding in fibrous long spacing collagen revealed by atomic force microscopy.
The influence of alpha1-acid glycoprotein on the formation of fibrous long spacing fibers of collagen has been investigated. It was observed that addition of the glycoprotein to dialyzed collagen solutions caused a significant decrease in the intensity of the circular dichroic spectrum of collagen. This phenomenon, which displays an optimum with respect to glycoprotein, is consistent with previous observations of fibrous long spacing fiber formation. Changes in viscosity of collagen initially dissolved in acetic acid were monitored during dialysis. It was found that a significant increase in viscosity must occur during dialysis of collagen before fibrous long spacing formation could take place. This increase in viscosity can be related directly to removal of acetic acid from the collagen solution. Removal of all sialyl residues from the alpha1-acid glycoprotein with neuraminidase prevents fibrous long spacing formation while removal of up to 35% of the sialyl residues has no effect on the interaction of glycoprotein with collagen. Amino acid composition and radioactivity studies suggest that 45-55% of the insoluble fibrous long spacing fibers is glycoprotein. In contrast to native collagen fibers, reduced fibrous long spacing fibers do not contain histidinohydroxymerodesmosine or hydroxylysinonorleucine. Instead, they contain significant quantities of allysine aldol and epsilon-hydroxynorleucine.