Altuvia Y, Margalit H
Department of Molecular Genetics, The Hebrew University - Hadassah Medical School, Jerusalem, 91120, Israel.
J Mol Biol. 2000 Jan 28;295(4):879-90. doi: 10.1006/jmbi.1999.3392.
Proteasomal cleavage of proteins is the first step in the processing of most antigenic peptides that are presented to cytotoxic T cells. Still, its specificity and mechanism are not fully understood. To identify preferred sequence signals that are used for generation of antigenic peptides by the proteasome, we performed a rigorous analysis of the residues at the termini and flanking regions of naturally processed peptides eluted from MHC class I molecules. Our results show that both the C terminus (position P1 of the cleavage site) and its immediate flanking position (P1') possess significant signals. The N termini of the peptides show these signals only weakly, consistent with previous findings that antigenic peptides may be cleaved by the proteasome with N-terminal extensions. Nevertheless, we succeed to demonstrate indirectly that the N-terminal cleavage sites contain the same preferred signals at position P1'. This reinforces previous findings regarding the role of the P1' position of a cleavage site in determining the cleavage specificity, in addition to the well-known contribution of position P1. Our results apply to the generation of antigenic peptides and bare direct implications for the mechanism of proteasomal cleavage. We propose a model for proteasomal cleavage mechanism by which both ends of cleaved fragments are determined by the same cleavage signals, involving preferred residues at both P1 and P1' positions of a cleavage site. The compatibility of this model with experimental data on protein degradation products and generation of antigenic peptides is demonstrated.
蛋白质的蛋白酶体切割是大多数呈递给细胞毒性T细胞的抗原肽加工过程的第一步。然而，其特异性和机制尚未完全了解。为了确定蛋白酶体用于生成抗原肽的优选序列信号，我们对从MHC I类分子洗脱的天然加工肽的末端和侧翼区域的残基进行了严格分析。我们的结果表明，C末端（切割位点的P1位置）及其紧邻的侧翼位置（P1'）都具有显著信号。肽的N末端仅微弱地显示出这些信号，这与先前的发现一致，即抗原肽可能被带有N末端延伸的蛋白酶体切割。尽管如此，我们成功地间接证明了N末端切割位点在P1'位置含有相同的优选信号。这除了强化了切割位点P1位置在确定切割特异性方面的作用这一先前发现之外，还进一步证实了其作用。我们的结果适用于抗原肽的生成，并且对蛋白酶体切割机制具有直接影响。我们提出了一种蛋白酶体切割机制模型，通过该模型，切割片段的两端由相同的切割信号决定，涉及切割位点P1和P1'位置的优选残基。该模型与关于蛋白质降解产物和抗原肽生成的实验数据的兼容性得到了证明。
