Quantum-chemical study of the reaction mechanism of polypeptide UDP-GalNAc transferase 2, a retaining glycosyltransferase
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| Year of publication | 2012 |
| Type | Conference abstract |
| MU Faculty or unit | |
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| Description | Glycosylation of cell surface proteins plays a crucial role in cell communication and recognition. Alterations in glycan structures are linked to many diseases with the most prominent example being cancer. To understand the regulation of glycosylation and to be able to modify it, reaction mechanisms of involved glycosyltransferases have to be known. However, reaction mechanism of the configuration-retaining group of glycosyltransferases hasn't been sufficiently explained yet. For this reason we have chosen a retaining glycosyltransferase – polypeptide UDP-GalNAc transferase (ppGalNAcT) – as the subject of our quantum-chemical study. This enzyme catalyses the transfer of N-acetylgalactosamine moiety onto serine or threonine hydroxyls, forming the first bond of the so-called O-linked glycosylation pathway. Increased activity of ppGalNAcT has been found to enable metastasis of breast and colorectal cancer. We're studying human ppGalNAcT2 by a hybrid QM/MM approach using density functional theory for the important part of the active site. We have found that the commonly used Becke-Perdew functional completely fails to describe the shape of the potential energy surface, while the OPBE functional provides results in good agreement with state-of-the-art meta-hybrid functional M06-2X. Structures of reactant and product have been successfully obtained on the OPBE-D3/TZP level, enabling a 2D potential energy surface scan to locate the transition state candidates for final optimisation. Results suggest that the reaction proceeds via a one-step SNi mechanism, initiated by proton transfer from acceptor hydroxyl to donor phosphate. This conclusion agrees well with recent experimental evidence. |
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