Because the glycosaminoglycans have numerous negative charges, the chains repel each other and so the proteoglycan molecule is like a bristle brush.
(the glycosaminoglycans; have; numerous negative charges) (the chains; repel; each other) (the proteoglycan molecule; is; like a bristle brush)
the glycosaminoglycans the chains the proteoglycan molecule
have repel is
numerous negative charges
each other
like a bristle brush