Körner C, Herzog A, Weber B, Rosorius O, Hemer F, Schmidt B, Braulke T
Institute of Biochemistry II, University of Göttingen, Federal Republic of Germany.
J Biol Chem. 1994 Jun 17;269(24):16529-32.
Some steps in the receptor-mediated transport of newly synthesized mannose 6-phosphate-containing lysosomal enzymes are assumed to be accompanied by changes in the phosphorylation state of receptors. In vitro, the metabolically phosphorylated 46-kDa mannose 6-phosphate receptor (MPR 46) was dephosphorylated by protein phosphatase 2A. The synthetic cytoplasmic domain of MPR 46 was phosphorylated in vitro by casein kinase II. Tryptic phosphopeptide mapping showed that casein kinase II phosphorylates MPR 46 in vitro at the same site that is phosphorylated in vivo. Inhibition studies using synthetic peptides corresponding to different amino acid sequences of the cytoplasmic tail of MPR 46 revealed that the sequence 26-32 (ADGCDFV) contribute to efficient phosphorylation of serine 56. Baby hamster kidney cells were transfected with wild type human MPR 46 cDNA or cDNAs containing mutations in the cytoplasmic tail and assayed for their phosphorylation state in vivo. The phosphorylation of mutant receptors with deleted residues 23-28 (NLVADG) was strongly reduced. These data indicate that residues on the N-terminal side of the phosphorylatable serine 56 may influence the efficiency with which a casein-kinase II-like kinase phosphorylates MPR 46.
新合成的含甘露糖6-磷酸的溶酶体酶的受体介导转运中的某些步骤被认为伴随着受体磷酸化状态的变化。在体外，经代谢磷酸化的46 kDa甘露糖6-磷酸受体（MPR 46）被蛋白磷酸酶2A去磷酸化。MPR 46的合成细胞质结构域在体外被酪蛋白激酶II磷酸化。胰蛋白酶磷酸肽图谱显示，酪蛋白激酶II在体外使MPR 46磷酸化的位点与在体内磷酸化的位点相同。使用与MPR 46细胞质尾部不同氨基酸序列相对应的合成肽进行的抑制研究表明，序列26-32（ADGCDFV）有助于丝氨酸56的有效磷酸化。用野生型人MPR 46 cDNA或细胞质尾部含有突变的cDNA转染幼仓鼠肾细胞，并测定其在体内的磷酸化状态。缺失残基23-28（NLVADG）的突变受体的磷酸化显著降低。这些数据表明，可磷酸化丝氨酸56 N端一侧的残基可能影响酪蛋白激酶II样激酶使MPR 46磷酸化的效率。
