> Many post-translational modifications like glycosylation > (http://www.functionalglycomics.org/static/index.shtml)in proteins > fundamentally change the (functional) 'nature' of the protein (as also the > molecular structure of the protein in case of glycosylation through > addition of sugar chains (glycans)).
Absolutely, but I would go further and state that any chemical modification will change the fundamental type, and this will necessarily change dispositions to realizing certain functions. -=Michel=-