Structural Snapshots of α‐1,3‐Galactosyltransferase with Native Substrates: Insight into the Catalytic Mechanism of Retaining Glycosyltransferases

다국어 초록 (Multilingual Abstract)

Glycosyltransferases (GTs) are a key family of enzymes that catalyze the synthesis of glycosidic bonds in all living organisms. The reaction involves the transfer of a glycosyl moiety and can proceed with retention or inversion of the anomeric configuration. To date, the catalytic mechanism of retaining GTs is a topic of great controversy, particularly for those enzymes containing a putative nucleophilic residue in the active site, for which the occurrence of a double‐displacement mechanism has been suggested. We report native ternary complexes of the retaining glycosyltransferase α‐1,3‐galactosyltransferase (α3GalT) from Bos taurus, which contains such a nucleophile in the active site, in a productive mode for catalysis in the presence of its sugar donor UDP‐Gal, the acceptor substrate lactose, and the divalent cation cofactor. This new experimental evidence supports the occurrence of a front‐side substrate‐assisted SNi‐type reaction for α3GalT, and suggests a conserved common catalytic mechanism among retaining GTs.
Kristallklar: Für den nativen ternären Komplex der α‐1,3‐Galactosyl‐Transferase (α3GalT) aus der GT6‐Familie der Glykosyltransferasen wurde die Kristallstruktur mit einem vermuteten Nukleophil in einer katalytisch produktiven Anordnung im aktiven Zentrum gelöst. Die Konfiguration des aktiven Zentrums spricht für einen substratunterstützten Vorderseitenangriff (SNi) und deutet auf einen konservierten Mechanismus in konfigurationserhaltenden Glykosyltransferasen hin.