An acetylation site in lectin domain modulates the biological activity of polypeptide GalNAc-transferase-2

NATACHA ZLOCOWSKI; VIRGINIA LORENZ; ERIC P. BENNETT; HENRIK CLAUSEN; NORES, GUSTAVO A.; FERNANDO J. IRAZOQUI

BIOLOGICAL CHEMISTRY

WALTER DE GRUYTER & CO

Lugar: Berlin; Año: 2013 vol. 394 p. 69 - 77

1431-6730

Polypeptide GalNAc-transferases (ppGalNAc-Ts)are a family of enzymes that catalyze the initiation of mucintypeO -glycosylation. All ppGalNAc-T family memberscontain a common (QXW) 3 motif, which is present in theR-type lectin group. The acetylation site K521 is part of theQKW motif of β -trefoil in the lectin domain of ppGalNAcT2.We used a combination of acetylation and site-directedmutagenesis approaches to examine the functional roleof K521 in ppGalNAc-T2. Binding assays of non-acetylatedand acetylated forms of the mutant ppGalNAc-T2 K521Q tovarious naked and α GalNAc-glycosylated mucin peptidesindicated that the degree of interaction of lectin domainwith α GalNAc depends on the peptide sequence of mucin.Studies of the inhibitory effect of various carbohydrates onthe interactions of ppGalNAc-T2 with MUC1 α GalNAc indicatethat point K521Q mutation enhance the carbohydratespecificity of lectin domain for α GalNAc. K521Q mutationresulted in an enzyme activity lower than that of the wildtypeppGalNAc-T2, similar to the acetylation of ppGalNAcT2.We conclude that an acetylation site in the QKW motifof the lectin domain modulates carbohydrate recognitionspecificity and catalytic activity of ppGalNAc-T2 forpartially preglycosylated acceptors and a certain nakedpeptide. Posttranslational modifications of ppGalNAcTs,such as acetylation, may play key roles in modulatingthe functions of the R-type lectin domains in cellularhomeostasis.