Kuckelkorn U, Frentzel S, Kraft R, Kostka S, Groettrup M, Kloetzel P M
Institut für Biochemie, Charité, Humboldt Universität zu Berlin, Germany.
Eur J Immunol. 1995 Sep;25(9):2605-11. doi: 10.1002/eji.1830250930.
The 20S proteasome is the enzyme complex responsible for the processing of antigens bound by major histocompatibility complex class I molecules. The role of the interferon-gamma (IFN-gamma)-inducible proteasome subunits LMP2 and LMP7 in this process is, however, still controversial. We have studied the effects of IFN-gamma-independent LMP incorporation on the quality of peptides processed from the murine cytomegalovirus IE pp89 25-mer polypeptide substrate through dual cleavages by 20S proteasomes. The incorporation of a single LMP subunit or both LMP2 and LMP7 induces changes in 20S proteasome subunit stoichiometry, alters its cleavage site preference and in consequence, the quality of the generated peptides. When the several hydrolytic activities are tested with short fluorogenic peptide substrates, the Vmax, S0.5 (Km), or both values of 20S proteasomes are altered, depending on the combination of LMP. There exists, however, no obvious correlation between the observed changes in hydrolytic activities against short fluorogenic peptides and the changes in dual cleavage site usage within the 25-mer polypeptide substrate. As judged from the calculated Hill coefficients, the presence of both LMP subunits induces a drastic increase in positive cooperativity between the proteasome subunits.
20S蛋白酶体是负责处理与主要组织相容性复合体I类分子结合的抗原的酶复合物。然而，干扰素-γ（IFN-γ）诱导的蛋白酶体亚基LMP2和LMP7在此过程中的作用仍存在争议。我们研究了不依赖IFN-γ的LMP掺入对通过20S蛋白酶体的双重切割从鼠巨细胞病毒IE pp89 25聚体多肽底物加工的肽质量的影响。单个LMP亚基或LMP2和LMP7两者的掺入都会诱导20S蛋白酶体亚基化学计量的变化，改变其切割位点偏好，进而改变所产生肽的质量。当用短的荧光肽底物测试几种水解活性时，20S蛋白酶体的Vmax、S0.5（Km）或两者的值会发生改变，这取决于LMP的组合。然而，观察到的针对短荧光肽的水解活性变化与25聚体多肽底物内双重切割位点使用的变化之间没有明显的相关性。根据计算的希尔系数判断，两个LMP亚基的存在会导致蛋白酶体亚基之间的正协同性急剧增加。
