NAG, FUC molecules in PDB files
The insulin receptor is a glycoprotein. This is discussed, albeit briefly, in both papers for the structures you mentioned and the glycosylation is visible in the structures themselves. You can get more info in the following paper, among others:

Sparrow LG, Lawrence MC, Gorman JJ, Strike PM, Robinson CP, McKern NM, Ward CW. 2008. N-linked glycans of the human insulin receptor and their distribution over the crystal structure. Proteins 71(1):426-439.