Role for MHC class I molecules in selecting and protecting high affinity peptides in the presence of proteases.
Role for MHC class I molecules in selecting and protecting high affinity peptides in the presence of proteases.
复制标题
MHC I 类分子在蛋白酶存在下选择和保护高亲和力肽的作用。
DOI：
10.4049/jimmunol.152.6.2798
复制
发表时间：
1994
影响因子：
4.4
通讯作者：
P. Kourilsky
中科院分区：
文献类型：
--
作者：
D. Ojcius;P. Langlade‐Demoyen;G. Gachelin;P. Kourilsky
来自胞浆的银片段被运输到内质网(ER)腔内，在那里它们与新生的MHC I类分子结合。然而，目前尚不清楚是否只有高亲和力的多肽进入内质网，或者内质网蛋白酶是否必须将较长的前体多肽削减到最佳大小。为了评价体外蛋白水解性精细剪裁的可行性，将可溶性KD和KB与KD或KB结合的多肽预先孵育，并将混合物暴露于三种不同的蛋白酶。I类保护等位基因特异性多肽不被蛋白质降解，而其他多肽被降解到氨基酸水平。当KD/S11E(SYIPSAEYILE)与羧肽酶孵育后免疫沉淀时，发现S11E和最适大小的S9I(SYIPSAEYI)都与KD特异结合。然而，当S11E、KD和羧基肽酶同时作用时，S91仅被回收，而如果使用较高的蛋白酶浓度和较短的蛋白分解时间，则没有对结合的S11E进行细微的修剪，这表明修剪只发生在非结合状态。KD/S11E经羧基肽酶处理后，与KD免疫共沉淀的多肽数量增加，表明多肽亲和力增强。KD还通过裂解的微生物体制剂保护S9I不被蛋白质降解，表明I类在体内也能保护高亲和力的多肽。这些结果表明，I类参与了内质网中高亲和力多肽的选择，通过采样运输的游离肽被内质网酶降解或外排回胞浆。
Ag fragments derived from the cytosol are transported into the endoplasmic reticulum (ER) lumen, where they bind to nascent MHC class I molecules. However, it is not known whether only high affinity peptides enter the ER, or whether ER proteases must trim longer precursor peptides down to optimal size. To evaluate the feasibility of proteolytic fine trimming in vitro, soluble Kd and Kb were preincubated with peptides that bind to Kd or Kb and the mixture was exposed to three different proteases. Class I protected allele-specific peptides against proteolysis, whereas the other peptides were degraded to the amino acid level. When a Kd/S11E (SYIPSAEYILE) complex was immunoprecipitated after incubation with carboxypeptidase, both S11E and the optimal sized S9I (SYIPSAEYI) were found to be specifically bound to Kd. However, only S91 was recovered if S11E, Kd and carboxypeptidase were mixed at the same time, and there was no fine-trimming of bound S11E if high protease concentrations and short proteolysis times were used, which suggests that trimming occurs only in the unbound state. The amount of peptide that immunoprecipitated with Kd increased after carboxypeptidase treatment of Kd/S11E, implying that the peptide affinity had increased. Kd also protected S9I against proteolysis by a lysed microsome preparation, demonstrating that class I could also protect high affinity peptides in vivo. These results suggest that class I participates in the selection of high affinity peptides in the ER, by sampling transported unbound peptides are degraded by ER proteases or efflux back to the cytosol.