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Glycosylation of the enhanced aromatic sequon is similarly stabilizing in three distinct reverse turn contexts

Price, Joshua L., Powers, David L., Powers, Evan T., Kelly, Jeffery W.
Proceedings of the National Academy of Sciences of the United States of America 2011 v.108 no.34 pp. 14127-14132
biopharmaceuticals, glycosylation, guidelines, protein folding, proteins
Cotranslational N-glycosylation can accelerate protein folding, slow protein unfolding, and increase protein stability, but the molecular basis for these energetic effects is incompletely understood. N-glycosylation of proteins at naïve sites could be a useful strategy for stabilizing proteins in therapeutic and research applications, but without engineering guidelines, often results in unpredictable changes to protein energetics. We recently introduced the enhanced aromatic sequon as a family of portable structural motifs that are stabilized upon glycosylation in specific reverse turn contexts: a five-residue type I β-turn harboring a G1 β-bulge (using a Phe–Yyy–Asn–Xxx–Thr sequon) and a type II β-turn within a six-residue loop (using a Phe–Yyy–Zzz–Asn–Xxx–Thr sequon) [Culyba EK, et al. (2011) Science 331:571–575]. Here we show that glycosylating a new enhanced aromatic sequon, Phe–Asn–Xxx–Thr, in a type I' β-turn stabilizes the Pin 1 WW domain. Comparing the energetic effects of glycosylating these three enhanced aromatic sequons in the same host WW domain revealed that the glycosylation-mediated stabilization is greatest for the enhanced aromatic sequon complementary to the type I β-turn with a G1 β-bulge. However, the portion of the stabilization from the tripartite interaction between Phe, Asn(GlcNAc), and Thr is similar for each enhanced aromatic sequon in its respective reverse turn context. Adding the Phe–Asn–Xxx–Thr motif (in a type I' β-turn) to the enhanced aromatic sequon family doubles the number of proteins that can be stabilized by glycosylation without having to alter the native reverse turn type.