Boehncke W H, Takeshita T, Pendleton C D, Houghten R A, Sadegh-Nasseri S, Racioppi L, Berzofsky J A, Germain R N
Lymphocyte Biology Section, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892.
J Immunol. 1993 Jan 15;150(2):331-41.
Previous studies on the role of specific residues of the peptide or MHC molecule in Ag presentation have revealed the sensitivity of this complex system to even small changes in structure. In our study, we have analyzed the effect of amino acid substitution in a major CD4+ T cell determinant (T1) of HIV-1 gp160 on binding and recognition in the context of various E alpha E beta MHC class II molecules. Individual alanine substitutions at all but three positions had little or no negative effect on either MHC binding or recognition by a specific T hybridoma, whereas substitutions with larger side chains often diminished reactivity. A poly-alanine peptide containing only four of the original residues was an effective MHC class II binder and in vivo immunogen, although lacking the ability to stimulate the hybridoma. Replacement of a glutamic acid in T1 with alanine or a size-conservative, uncharged glutamine, but not a negatively charged aspartic acid produced a peptide at least 100-fold more potent than the parent peptide, indicating an inhibitory effect of the negative charge. Conversely, substitution of a glutamic acid for valine at position 29 in the floor of the peptide binding site of the E alpha E beta molecule decreased functional presentation of this peptide by more than 2 logs. However, these two effects of glutamic acid were not complementary and were mediated by distinct mechanisms, as the change in the peptide altered the extent of binding to class II, but the change in the MHC molecule decreased recognition without inhibiting peptide binding. Taken together, the data all suggest the conclusion that changes in side-chains of peptides and MHC molecules affect Ag presentation and T cell stimulation most often by introducing dominant negative or interfering groups that prevent or alter the pattern of binding events primarily mediated by a very limited number of other residues in the Ag or presenting molecule. These results have important implications for understanding the biochemistry of peptide-MHC-TCR interactions and for the possible design of vaccines both more potent and less subject to allele-specific limitations on immunogenicity.
先前关于肽或MHC分子的特定残基在抗原呈递中的作用的研究表明，这个复杂系统对结构上即使很小的变化也很敏感。在我们的研究中，我们分析了HIV-1 gp160的主要CD4+ T细胞决定簇（T1）中的氨基酸替换对在各种EαEβ MHC II类分子背景下的结合和识别的影响。除了三个位置外，在所有其他位置进行单个丙氨酸替换对MHC结合或特定T杂交瘤的识别几乎没有或没有负面影响，而用较大侧链进行替换通常会降低反应性。一个仅包含四个原始残基的聚丙氨酸肽是一种有效的MHC II类结合剂和体内免疫原，尽管缺乏刺激杂交瘤的能力。用丙氨酸或大小保守的不带电荷的谷氨酰胺取代T1中的谷氨酸，但不是带负电荷的天冬氨酸，产生的肽比亲本肽的效力至少高100倍，表明负电荷具有抑制作用。相反，在EαEβ分子的肽结合位点底部的第29位用谷氨酸替换缬氨酸使该肽的功能呈递降低了超过2个对数。然而，谷氨酸的这两种作用不是互补的，并且是由不同的机制介导的，因为肽的变化改变了与II类的结合程度，但MHC分子的变化在不抑制肽结合的情况下降低了识别。综上所述，数据都表明这样的结论：肽和MHC分子侧链的变化最常通过引入显性负性或干扰基团来影响抗原呈递和T细胞刺激，这些基团会阻止或改变主要由抗原或呈递分子中非常有限数量的其他残基介导的结合事件模式。这些结果对于理解肽-MHC-TCR相互作用的生物化学以及对于可能设计出更有效且较少受免疫原性等位基因特异性限制的疫苗具有重要意义。
