Good morning, Bernhard, I do not think that you had pure luck (though serendipity helps a lot). You said that the PNGaseF treated protein was indeed stable, that was already a good hint.
In my little experience with N- and O-glycoproteins, with not a high percentage of sugar content, I saw a difference. N-glycosylated proteins with Asn mutated to Asp tend to be more stable, because you are putting negative charges on the surface. O-glycosylated proteins expressed unglycosylated or mutated do not gain in stability, and are prone to precipitation (whenever they are expressed). This is possibly due to the fact that -OH on the surface have not the same effect as the negative charges. Moreover, in the few entries in the PDB with O-linked sugars, these seems to be like un umbrella, covering/masking a larger portion of the protein's surface. Hence trimming the sugars off will expose potentially "sticky" parts. That's my 2 cents. Best regards, Adriana
