Mucin-type O-glycosylation is an evolutionarily conserved and essential post-translational protein modification that is initiated in the Golgi apparatus by a family of enzymes known as the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts). GalNAc-Ts are type II membrane proteins which contain short N-terminal tails located in the cytoplasm, a transmembrane domain that crosses the Golgi membrane, to which is connected a stem region that tethers the C-terminal catalytic and lectin domains that reside in the Golgi lumen. Although mucin-type O-glycans have been shown to play critical roles in numerous biological processes, little is known about how the GalNAc-Ts are targeted to their site of action within the Golgi complex. Here, we investigate the essential protein domains required for Golgi localization of four representative members of the GalNAc-T family of enzymes. We find that GalNAc-T1 and -T2 require their cytoplasmic tail and transmembrane domains for proper Golgi localization, while GalNAc-T10 requires its transmembrane and luminal stem domains. GalNAc-T7 can use either its cytoplasmic tail or its luminal stem, in combination with its transmembrane domain, to localize to the Golgi. We determined that a single glutamic acid in the GalNAc-T10 cytoplasmic tail inhibits its ability to localize to the Golgi via a cytoplasmic tail-dependent mechanism. We therefore demonstrate that despite their similarity, different members of this enzyme family are directed to the Golgi by more than one set of targeting signals.

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GalNAc-T酶家族的成员利用独特的高尔基体定位机制

粘蛋白型O-糖基化是一种进化上保守的必需翻译后蛋白质修饰，其在高尔基体中由称为UDP-GalNAc：多肽N-乙酰半乳糖胺基转移酶（GalNAc-Ts）的酶家族引发。GalNAc-Ts是II型膜蛋白，在细胞质中含有短的N末端尾巴，该尾巴穿过高尔基体膜，跨膜结构域连接了一个茎区域，该区域束缚了位于细胞质中的C末端催化和凝集素结构域。高尔基体腔。虽然粘蛋白型O-聚糖已被证明在众多生物过程中起关键作用，人们对GalNAc-T如何靶向其在高尔基体中的作用位点知之甚少。在这里，我们研究了GalNAc-T酶家族的四个代表性成员高尔基体定位所需的必需蛋白质结构域。我们发现，GalNAc-T1和-T2需要它们的胞质尾部和跨膜结构域才能进行正确的高尔基体定位，而GalNAc-T10则需要其跨膜结构和腔内茎结构域。GalNAc-T7可以使用其胞质尾巴或其腔茎及其跨膜结构域来定位高尔基体。我们确定，GalNAc-T10细胞质尾巴中的单个谷氨酸可通过细胞质尾巴依赖性机制抑制其定位于高尔基体的能力。