Conformational Preferences for N-Glycans at the Surface of CEACAM1-Ig1

Glycans on glycoproteins play roles that range from quality control in protein folding, to mediation of interactions with other proteins, to stabilization of the protein to which they are attached. Computation can suggest structures that underlie these roles, but confidence is limited by the accuracy of energetic calculations and their applicability to the aqueous environment in which proteins function. Experimental validation of suggested structures is therefore of primary importance. Here we use NMR data, including long-range pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs), to screen structures produced by a version of accelerated molecular dynamics (Pep-GaMD). This version was designed to improve the search for peptide-protein interactions, but here it is successfully applied to glycans attached to a target protein. The target protein, the N-terminal domain of human CEACAM1, is expressed with homogeneous GlcNAc₂Man₅ glycans at its three N-glycosylation sites. One site (N104) is found to have preferred conformations that exploit hydrophobic interactions between its glycans and protein hydrophobic residues, potentially adding to protein stability and protection from adverse interactions.