Non-enzymatic glycation of type I collagen occurs in aging and diabetes, and may affect collagen solubility, charge, polymerization, and intermolecular interactions. Proteoglycans1 (PGs) bind type I collagen and are proposed to regulate fibril assembly, function, and cell-collagen interactions. Moreover, on the collagen fibril a keratan sulfate (KS) PG binding region overlaps with preferred collagen glycation sites. Thus, we examined the effect of collagen modified by simple glycation on PG-collagen interactions. By affinity coelectrophoresis (ACE), we found reduced affinities of heparin and KSPGs for glycated but not normal collagen, whereas the dermatan sulfate (DS)PGs decorin and biglycan bound similarly to both, and that the affinity of heparin for normal collagen decreased with increasing pH. Circular dichroism (CD) spectroscopy revealed normal and glycated collagens to assume triple helical conformations, but heparin addition caused precipitation and decreased triple helical content - effects that were more marked with glycated collagen. A spectrophotometric assay revealed slower polymerization of glycated collagen. However, ultrastructural analyses indicated that fibrils assembled from normal and glycated collagen exhibited normal periodicity, and had similar structures and comparable diameter distributions. B-cells expressing the cell surface heparan sulfate PG syndecan-1 adhered well to normal but not glycated collagen, and endothelial cell migration was delayed on glycated collagen. We speculate that glycation diminishes the electrostatic interactions between type I collagen and PGs, and may interfere with core protein-collagen associations for KSPGs but not DSPGs. Therefore in vivo, collagen glycation may weaken PG-collagen interactions, thereby disrupting matrix integrity and cell-collagen interactions, adhesion, and migration. © 2008 Wiley-Liss, Inc.