Glycation changes the charge distribution of type I collagen fibrils

In aging and diabetes, glycation of collagen molecules leads to the formation of cross-links that could alter the surface charge on collagen fibrils, and hence affect the properties and correct functioning of a number of tissues. The electron-optical stain phosphotungstic acid (PTA) binds to positively charged amino acid side-chains and leads to the characteristic banding pattern of collagen seen in the electron microscope; any change in the charge on these side-chains brought about by glycation will affect the uptake of PTA. We found that, upon glycation, a decrease in stain uptake was observed at up to five regions along the collagen D-period; the greatest decrease in stain uptake was apparent at the c1 band. This reduction in PTA uptake indicates that the binding of fructose leads to an alteration in the surface charge at several sites along the D-period. Not all lysine and arginine residues are involved; there appear to be specific residues that suffer a loss of positive charge.