In both structure determination where one desires to express proteins in E. coil and studies of glycan function where one desires to maintain structure of glycoprotiens while particular glycans are removed, it is useful to have non-glycan subsitiutes in protein expression. The following article demonstrates that substitution of certain amino acids in and around N-glycosylation sites sometimes works.

Uemura et al. Glycobiology 16 258-270

It is suggested that the effects relate to maintaining conformation, but there seems to be no pattern to the substitutions (positive, neutral and negative side chains are represented) and there is no structural data that I know of. I would be very interested in knowing of such data or other opinions regarding how this substitution (or other substitutions) preserve function.