Panzer P, Preuss U, Joberty G, Naim H Y
Protein Secretion Group, Institute of Microbiology, Heinrich Heine University of Düsseldorf, Universitätsstrasse 1, Geb. 26.12.01, D-40225 Düsseldorf, Germany.
J Biol Chem. 1998 May 29;273(22):13861-9. doi: 10.1074/jbc.273.22.13861.
The roles of various domains of intestinal lactase-phlorizin hydrolase (pro-LPH) on its folding, dimerization, and polarized sorting are investigated in deletion mutants of the ectodomain fused or not fused with the membrane-anchoring and cytoplasmic domains (MACT). Deletion of 236 amino acids immediately upstream of MACT has no effect on the folding, dimerization, transport competence, or polarized sorting of the mutant LPH1646MACT. By contrast, LPH1646, an anchorless counterpart of LPH1646MACT, is not transported beyond the ER and persists as a mannose-rich monomer during its entire life cycle. The further deletion of 87 amino acids generates a correctly folded but transport-incompetent monomeric LPH1559MACT mutant. The results strongly suggest that dimerization and transport of pro-LPH implicate a stretch of 87 amino acids in the ectodomain between LPH1646MACT and LPH1559MACT. In addition, dimerization of pro-LPH requires at least two further criteria: (i) a correctly folded ectodomain of pro-LPH and (ii) the presence of the transmembrane region. Neither of these requirements alone is sufficient for dimerization. Finally, the sorting of pro-LPH appears to be mediated by signals located between the cleavage site of pro-LPH and the LPH1646MACT mutant.
在与膜锚定和细胞质结构域（MACT）融合或未融合的胞外结构域缺失突变体中，研究了肠乳糖酶 - 根皮苷水解酶（前体LPH）各个结构域在其折叠、二聚化和极化分选过程中的作用。在MACT上游紧邻的236个氨基酸缺失，对突变体LPH1646MACT的折叠、二聚化、转运能力或极化分选没有影响。相比之下，LPH1646MACT的无锚定对应物LPH1646，在其整个生命周期中都不会转运到内质网之外，而是以富含甘露糖的单体形式持续存在。进一步缺失87个氨基酸会产生一个正确折叠但无转运能力的单体LPH1559MACT突变体。结果强烈表明，前体LPH的二聚化和转运涉及LPH1646MACT和LPH1559MACT之间胞外结构域中的一段87个氨基酸。此外，前体LPH的二聚化至少还需要另外两个条件：（i）前体LPH正确折叠的胞外结构域和（ii）跨膜区域的存在。这两个条件单独存在都不足以实现二聚化。最后，前体LPH的分选似乎是由位于前体LPH裂解位点和LPH1646MACT突变体之间的信号介导的。
