Nelson C A, Vidavsky I, Viner N J, Gross M L, Unanue E R
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Proc Natl Acad Sci U S A. 1997 Jan 21;94(2):628-33. doi: 10.1073/pnas.94.2.628.
Major histocompatibility complex (MHC) class II molecules bind antigenic peptides for display to T lymphocytes. Although the enzymes involved remain to be identified, it is commonly believed that class II associated peptides are released from intact antigens through a series of proteolytic steps carried out inside antigen presenting cells. We have examined the effect of amino acid substitutions on proteolytic processing of the model antigen hen-egg lysozyme (HEL). Altered HEL molecules, engineered by site-directed mutagenesis of a HEL cDNA, were expressed as separate stable transfectants in a B cell lymphoma line. Each transfectant processed a different mutant HEL protein for presentation on MHC class II. We purified the resulting class II-associated peptides and analyzed them by mass spectrometry. Our results strongly support the hypothesis that antigen processing continues after peptide binding to the MHC class II molecule and are most consistent with a scenario in which long peptides first bind to MHC class II and are then trimmed by exopeptidase.
主要组织相容性复合体（MHC）II类分子结合抗原肽以呈递给T淋巴细胞。尽管相关酶仍有待确定，但人们普遍认为II类相关肽是通过抗原呈递细胞内进行的一系列蛋白水解步骤从完整抗原中释放出来的。我们研究了氨基酸取代对模型抗原鸡卵溶菌酶（HEL）蛋白水解加工的影响。通过对HEL cDNA进行定点诱变构建的经改变的HEL分子，在B细胞淋巴瘤系中作为单独的稳定转染子表达。每个转染子加工不同的突变型HEL蛋白以在MHC II类分子上呈递。我们纯化了产生的II类相关肽，并通过质谱分析它们。我们的结果有力地支持了这样一种假说，即抗原加工在肽与MHC II类分子结合后仍在继续，并且与长肽首先结合到MHC II类分子然后被外肽酶修剪的情况最为一致。
