The structure of the colorectal cancer-associated enzyme GalNAc-T12 reveals how nonconserved residues dictate its function
The structure of the colorectal cancer-associated enzyme GalNAc-T12 reveals how nonconserved residues dictate its function
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DOI：
10.1073/pnas.1902211116
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发表时间：
2019-10-08
影响因子：
11.1
通讯作者：
Samara, Nadine L.
中科院分区：
文献类型：
--
作者：
Fernandez, Amy J.;Daniel, Earnest James Paul;Samara, Nadine L.
多肽N-乙酰半乳糖胺转移酶（GalNAc-Ts）通过催化N-乙酰半乳糖胺（GalNAc）转移到蛋白质底物上的Ser或Thr来启动粘蛋白型O-糖基化。同工酶GalNAc-T12的非活性和部分活性变体存在于结直肠癌患者的亚组中，并且这些变体中的几个改变具有未知功能的非保守残基。虽然先前的生物化学研究已经证明GalNAc-T12通过与其催化和凝集素结构域的独特相互作用选择肽和糖肽底物，但是这种独特底物选择性的分子基础仍然难以捉摸。在这里，我们研究GalNAc-T12的活性和底物选择性的分子基础。与二糖基化肽底物复合的GalNAc-T12的X射线晶体结构揭示了GalNAc-T12催化结构域中的非保守GalNAc结合口袋如何决定其独特的底物选择性。此外，该结构提供了对结直肠癌突变如何破坏GalNAc-T12活性的深入了解，并说明了决定GalNAc-T12功能的规则如何与其他GalNAc-T不同。
Polypeptide N-acetylgalactosaminyl transferases (GalNAc-Ts) initiate mucin type O-glycosylation by catalyzing the transfer of N-acetylgalactosamine (GalNAc) to Ser or Thr on a protein substrate. Inactive and partially active variants of the isoenzyme GalNAc-T12 are present in subsets of patients with colorectal cancer, and several of these variants alter nonconserved residues with unknown functions. While previous biochemical studies have demonstrated that GalNAc-T12 selects for peptide and glycopeptide substrates through unique interactions with its catalytic and lectin domains, the molecular basis for this distinct substrate selectivity remains elusive. Here we examine the molecular basis of the activity and substrate selectivity of GalNAc-T12. The X-ray crystal structure of GalNAc-T12 in complex with a di-glycosylated peptide substrate reveals how a nonconserved GalNAc binding pocket in the GalNAc-T12 catalytic domain dictates its unique substrate selectivity. In addition, the structure provides insight into how colorectal cancer mutations disrupt the activity of GalNAc-T12 and illustrates how the rules dictating GalNAc-T12 function are distinct from those for other GalNAc-Ts.