Chaperone-Like Functions of N-Glycans in the Formation and Stabilization of Protein Conformation.

This article deals with the chaperone-like functions of N-glycans, laying stress on the fact that the information accumulated mostly by in vitro studies has clarified the general relationship between the functions and structures of N-glycans. High-mannose N-glycans, especially of large size, directly promote protein folding and subunit assembly as their major functions, and they also stabilize the resulting protein conformation in some degree. On the other hand, complex-type N-glycans fulfil the serious requirements for the stabilization of the functional conformation of parent proteins through their hydrophobic interactions with the hydrophobic protein surface unfavorable for protein stability. Newly acquired knowledge about the molecular bases underlying these functions confirms the view that a full understanding of N-glycan-protein interactions is essential for solid progress in medical science and protein engineering. Lastly, and most important, the possible function of high-mannose N-glycans in the direct promotion of the folding of nascent polypeptides in endoplasmic reticulum is discussed in connection with the calnexin and calreticulin functions widely accepted.