26S proteasomes and immunoproteasomes produce mainly N-extended versions of an antigenic peptide
26S proteasomes and immunoproteasomes produce mainly N-extended versions of an antigenic peptide
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DOI：
10.1093/emboj/20.10.2357
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发表时间：
2001-05-15
期刊：
影响因子：
11.4
通讯作者：
Goldberg, AL
中科院分区：
文献类型：
--
作者：
Cascio, P;Hilton, C;Goldberg, AL
蛋白酶体降解蛋白质是MHC I类分子上呈递的大多数抗原肽的来源。为了确定蛋白酶体是否直接产生这些肽或更长的前体，我们开发了新的方法来测量26 S和20 S颗粒在蛋白质降解过程中产生呈递表位或潜在前体的效率。卵白蛋白被26 S和20 S蛋白酶体分解产生免疫显性肽SIINFEKL，但主要产生含有1-7个额外的N-末端残基的变体。卵白蛋白分子被消化的次数中仅6-8%产生SIINFEKL或N-延伸形式。令人惊讶的是，含有干扰素-γ-诱导的β-亚基并且在抗原呈递中更有效的免疫蛋白酶体并不比蛋白酶体产生更多的SIINFEKL。然而，免疫蛋白酶体释放2-4倍的某些N-延伸版本。这些观察结果表明，免疫蛋白酶体的切割特异性的变化不仅影响C-末端，而且还影响潜在的抗原肽的N-末端，并表明大多数MHC呈递的肽是由氨基肽酶（例如，干扰素-γ诱导的酶亮氨酸氨基肽酶）对较大蛋白酶体产物的N-末端修剪引起的。
Protein degradation by proteasomes is the source of most antigenic peptides presented on MHC class I molecules. To determine whether proteasomes generate these peptides directly or longer precursors, we developed new methods to measure the efficiency with which 26S and 20S particles, during degradation of a protein, generate the presented epitope or potential precursors. Breakdown of ovalbumin by the 26S and 20S proteasomes yielded the immunodominant peptide SIINFEKL, but produced primarily variants containing 1-7 additional N-terminal residues, Only 6-8% of the times that ovalbumin molecules were digested was a SIINFEKL or an N-extended version produced. Surprisingly, immunoproteasomes which contain the interferon-gamma -induced beta -subunits and are more efficient in antigen presentation, produced no more SIINFEKL than proteasomes. However, the immunoproteasomes released 2-4 times more of certain N-extended versions. These observations show that the changes in cleavage specificity of immunoproteasomes influence not only the C-terminus, but also the N-terminus of potential antigenic peptides, and suggest that most MHC-presented peptides result from N-terminal trimming of larger proteasome products by aminopeptidases (e,g, the interferon-gamma -induced enzyme leucine aminopeptidase).