Recombinant protein expression using eukaryotic expression systems has certain advantages, such as addition of posttranslational modifications that help protein stability and activity. Asparagine-linked sugar attachment is one of the most common posttranslation modifications. However, sugar modification can impede the growth of high-quality protein crystals for structural studies using X-ray crystallography. To overcome this problem, consensus sites of N-linked attachments can be mutated into other similar residues, such as aspartic acid. Alternatively, enzymatic deglycosylation can be used to remove sugars. Peptide-N-Glycosidase F (PNGase F; EC 126.96.36.199) and Endoglycosidase H (Endo H; EC 188.8.131.52) are the most popular enzymes for this purpose.