Dong Feng, Sharma Jyotika, Xiao Yanming, Zhong Youmin, Zhong Guangming
Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
Infect Immun. 2004 Jul;72(7):3869-75. doi: 10.1128/IAI.72.7.3869-3875.2004.
We previously identified a chlamydial protein designated CPAF (chlamydia protease/proteasome-like activity factor) that is secreted into host cell cytosol for degrading host transcription factors required for major histocompatibility complex antigen expression. Here we report that CPAF, synthesized as a 70-kDa proprotein, is processed into two fragments (designated CPAFn and CPAFc) to form intramolecular dimers that are much more stable than the naïve CPAF. Precipitation with antibodies that recognized CPAF dimers removed the proteolytic activity responsible for degrading host transcription factor RFX5 from chlamydia-infected host cell cytosol, while precipitation with antibodies that recognized free CPAF fragments alone did not remove this activity. Separation of CPAFn from CPAFc resulted in a loss of proteolytic activity. Furthermore, neither expressed full-length CPAF that was not processed nor coexpressed CPAFn and CPAFc fragments that failed to form dimers degraded RFX5. These observations demonstrate that intramolecular dimerization is required for CPAF to degrade host transcription factors, a strategy that is utilized by an obligate intracellular bacterial species to evade host defenses.
我们之前鉴定出一种衣原体蛋白，命名为CPAF（衣原体蛋白酶/蛋白酶体样活性因子），它被分泌到宿主细胞胞质溶胶中，用于降解主要组织相容性复合体抗原表达所需的宿主转录因子。在此我们报告，CPAF最初作为一种70 kDa的前体蛋白合成，随后被加工成两个片段（分别命名为CPAFn和CPAFc），形成分子内二聚体，其稳定性远高于未加工的CPAF。用识别CPAF二聚体的抗体进行沉淀，可去除衣原体感染的宿主细胞胞质溶胶中负责降解宿主转录因子RFX5的蛋白水解活性，而仅用识别游离CPAF片段的抗体进行沉淀则不能去除该活性。将CPAFn与CPAFc分离会导致蛋白水解活性丧失。此外，未加工的全长CPAF或未能形成二聚体的共表达CPAFn和CPAFc片段均不能降解RFX5。这些观察结果表明，CPAF降解宿主转录因子需要分子内二聚化，这是一种专性胞内细菌用于逃避宿主防御的策略。
