Serine versus Threonine Glycosylation:  The Methyl Group Causes a Drastic Alteration on the Carbohydrate Orientation and on the Surrounding Water Shell

Abstract

Different behavior has been observed for the psi torsion angle of the glycosidic linkages of D-GalNAc-Ser and D-GalNAc-Thr motifs, allowing the carbohydrate moiety to adopt a completely different orientation. In addition, the fact that the water pockets found in alpha-D-GalNAc-Thr differ from those obtained for its serine analogue could be related to the different capability that the two model glycopeptides have to structure the surrounding water. This fact could have important biological inferences (i.e., antifreeze activity).

Deciphering the Non‐Equivalence of Serine and Threonine O‐Glycosylation Points: Implications for Molecular Recognition of the Tn Antigen by an anti‐MUC1 Antibody

“…In fact, in the SM3:1* complex, this linkage adopts the expected exo-anomeric/syn conformation, with f and y values of around 638 8 and 918 8,respectively. [9] This conformation is similar to that found for an on-related MUC1 glycopeptide bound to 237-mAb [21] (Figure 4b)a nd that exhibited for 1* bound to am odel lectin (Soybean agglutinin). [25] This geometry allows the formation of an intermolecular hydrogen bond between the hydroxymethyl group of GalNAc and the side chain of Ty r32L on the SM3 antibody.M oreover,t he N-acetyl group of the sugar stacks with the aromatic ring of Tr p33H, thus providing the impetus for the observed selectivity of SM3 for GalNAc-containing antigens.T his interaction is compatible with the previous solution NMR data.…”

“…[1,[4][5][6][7] Structural analysis of Tn antigen bound to its biological targets is thus of great significance for elucidating the mechanism of recognition, as well as for engineering novel antibodies and biosensors.I ng eneral, the Tn antigen is referred to as Nacetylgalactosamine (GalNAc) a-O-linked to serine (Ser) or threonine (Thr), without specifying which of the two amino acids the GalNAc is linked to.However,w ea nd others have observed the existence of subtly different conformational behaviors in solution of the basic Ser-a nd Thrcontaining structures. [8][9][10][11][12][13][14] Herein, we present adetailed analysis of the interaction of these two Tn determinants,a sM UC1 glycopeptides,t oa na nti-MUC1 antibody.M UC1 is ah eavily Oglycosylated membrane glycoprotein consisting of tandem repeats of 20 amino acids (AHGVTSAPDTRPAPG-STAPP), with five possible glycosylation sites. [15,16] This protein is overexpressed and partially glycosylated in cancer cells.C onsequently,s ome peptide fragments that are masked in healthy cells,s uch as APDTRP and their glycosylated analogues,a re now accessible and can interact with the immune system.…”

Recognition of the Thomsen-Friedenreich Pancarcinoma Carbohydrate Antigen by a Lamprey Variable Lymphocyte Receptor

“…This is somewhat atypical for sugar binding to proteins, where entropy is usually unfavorable due to loss of ligand conformational flexibility, and binding is enthalpically driven (24,26). In this regard, structural studies of small glycopeptides have shown that GalNAc␣ attached to serine and threonine prefer very different rotomer populations, both in solution (34) and in silico (35), which could affect binding thermodynamics.…”

Design and Synthesis of Antifreeze Glycoproteins and Mimics

“…[67] The involvement of the Thr residue in the hydration of AFGPs is supported by recent studies that have demonstrated that the Thr g-methyl group is an important determinant of both the carbohydrate orientation and the degree of hydration. [68] Replacement of d-GalNAcThr with d-GalNAcSer results in a significant increase in conformational degrees of freedom, and affects the strength of hydrogen bonding involving the N-acetyl group as well as the orientation of the surrounding water molecules. Thus, the evolution of AFGPs with Thr in their structure, rather than Ser, may be attributed to the contribution of Thr to hydrophobicity and hydration effects, as well as the restricted conformational space of Thr glycosides compared with Ser glycosides.…”