Carmicle Stephanie, Steede N Kalaya, Landry Samuel J
Department of Biochemistry, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
Mol Immunol. 2007 Feb;44(6):1159-68. doi: 10.1016/j.molimm.2006.06.014. Epub 2006 Aug 8.
Antigen three-dimensional structure potentially controls presentation of CD4(+) T-cell epitopes by limiting the access of proteolytic enzymes and MHC class II antigen-presenting proteins. The protease-sensitive mobile loops of Hsp10s from mycobacteria, Escherichia coli, and bacteriophage T4 (T4Hsp10) are associated with adjacent immunodominant helper T-cell epitopes, and a mobile-loop deletion in T4Hsp10 eliminated the protease sensitivity and the associated epitope immunodominance. In the present work, protease-sensitivity and epitope presentation was analyzed in a group of T4Hsp10 variants. Two mobile-loop sequence variants of T4Hsp10 were constructed by replacing different segments of the mobile loop with an irrelevant sequence from hen egg lysozyme. The variant proteins retained native-like structure, and the mobile loops retained protease sensitivity. Mobile-loop deletion and reconstruction affected the presentation of two epitopes according to whether the epitope was protease-independent or protease-dependent. The protease-independent epitope lies within the mobile loop, and the protease-dependent epitope lies in a well-ordered segment on the carboxy-terminal flank of the mobile loop. The results are consistent with a model for processing of the protease-dependent epitope in which an endoproteolytic nick in the mobile-loop unlocks T4Hsp10 three-dimensional structure, and then the epitope becomes available for binding to the MHC protein.
抗原的三维结构可能通过限制蛋白水解酶和MHC II类抗原呈递蛋白的接触来控制CD4(+) T细胞表位的呈递。来自分枝杆菌、大肠杆菌和噬菌体T4（T4Hsp10）的Hsp10s的蛋白酶敏感移动环与相邻的免疫显性辅助性T细胞表位相关，并且T4Hsp10中的移动环缺失消除了蛋白酶敏感性和相关的表位免疫显性。在本研究中，分析了一组T4Hsp10变体的蛋白酶敏感性和表位呈递情况。通过用来自鸡卵溶菌酶的无关序列替换移动环的不同片段，构建了T4Hsp10的两个移动环序列变体。变体蛋白保留了类似天然的结构，并且移动环保留了蛋白酶敏感性。根据表位是蛋白酶非依赖性还是蛋白酶依赖性，移动环的缺失和重建影响了两个表位的呈递。蛋白酶非依赖性表位位于移动环内，而蛋白酶依赖性表位位于移动环羧基末端侧翼的一个有序片段中。这些结果与蛋白酶依赖性表位加工模型一致，在该模型中，移动环中的内切蛋白水解切口解锁T4Hsp10的三维结构，然后表位可用于与MHC蛋白结合。
