>I do have one last question, if you don't mind. Would it be best to mutate an amino-acid such that it wouldn't needs PT modifications, or would it be best to find (or, God help me, engineer) a host that would perform these duties?
Well, you wouldn't have to worry about engineering your own strain of host cells for expression. Baculovirus expression systems in insect cell lines (High Five and Sf9) can handle most proteins from eukaryotes.
I would go to one of these expression systems. If you want to express in a prokaryotic system (BL21s or perhaps codon+), then you would have to look into playing around with constructs (chopping it up, etc.).
>Wouldn't the mutation affect the fold?
Certainly, that is a possibility. There are number of ways you can look into this, from computational (secondary structure prediction) to expression (mutant construct solubility) to functional (activity assay) to disorder (NMR, limited proteolysis).
>How useful would a crystal of a mutated protein be for subsequent analysis (especially, say, if glycosylation were needed for oligomer formation, which is still a big problem concerning my protein)?
It comes down to the question you are trying to answer with the crystal structure. Going off your assumption that glycosylation is needed for oligomerization, and further extrapolating that, say, oligomerization is needed for biological activity, then yes, you should present a crystal structure that is glycosylated, and functional assay that connects glycosylated oligomer to biological activity.
If the glycosylation has not effect on your particular system (say, the glycosylation is different from the oligomerization domain), again, you'll need biochemical and cell biological data to show that your construct still has activity.