艾滋病病毒(HIV)存在潜藏机制可以长期潜伏在细胞中而逃逸宿主免疫系统的攻击，目前已上市的抗HIV药物均不能选择性地杀伤感染细胞而根除病毒。新的研究思路对开发新型抗HIV药物显得非常重要，研究具有选择性地杀伤HIV感染细胞而保护正常细胞不受伤害的抗艾滋病药物是极有前景的方向。
核糖体失活蛋白(RIPs)具有RNA N-糖苷酶活性，可以阻遏了延长因子EF-1或EF-2与核糖体的结合，抑制蛋白质的生物合成。因此RIPs具有很高的细胞毒性，常常被开发成为免疫毒素、抗病毒和或抗肿瘤药物。RIP分为3类，I型、II型和III型。III型RIP以玉米RIP为代表，先合成无活性的含有一段25氨基酸的内部失活结构域的前体蛋白(PRO-RIP)，PRO-RIP被切除该结构域后才成为有活性的RIP (MOD)。香港中文大学邵鹏柱教授学科组与中国科学院昆明动物研究所动物模型与人类疾病机理重点实验室郑永唐研究员学科组合作对玉米RIP的内部失活结构域进行一系列的结构修饰和改造，获得了对HIV-1蛋白酶特异识别并激活的玉米RIP突变体。细胞水平实验的研究表明，突变体对未感染细胞毒性低，但突变体进入HIV-1感染细胞后则可被细胞内的HIV-1蛋白酶识别并切割去除失活结构域转变成为活性蛋白，从而选择性地杀伤HIV-1感染细胞。研究结果还表明，通过在玉米RIP突变体N端融合表达HIV-1 TAT蛋白的转导肽增加了突变体进入细胞的效率，对HIV-1感染细胞的杀伤力更强。玉米RIP突变体也可以被HIV-1蛋白酶耐药株的蛋白酶识别并激活，因此突变体对HIV-1蛋白酶耐药株感染细胞也有很好的选择杀伤性。该研究成果为研发特异性靶向HIV感染细胞的新型抗HIV药物提供了新思路和新策略。
研究成果在国际著名学术期刊Nucleic Acids Research 发表并申请了国家专利。相关研究获香港研究资助局、国家科技部973项目、国家重大科技专项、中国科学院等项目资助。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nucleic Acids Res. 2010 October; 38(19): 6803–6812.
doi: 10.1093/nar/gkq551.
A switch-on mechanism to activate maize ribosome-inactivating protein for targeting HIV-infected cells
Sue Ka-Yee Law,1 Rui-Rui Wang,2 Amanda Nga-Sze Mak,1 Kam-Bo Wong,1 Yong-Tang Zheng,2* and Pang-Chui Shaw1*
1Department of Biochemistry and Centre for Protein Science and Crystallography, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong and 2Key Laboratory of Animal Models and Human Disease Mechanisms, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
Maize ribosome-inactivating protein (RIP) is a plant toxin that inactivates eukaryotic ribosomes by depurinating a specific adenine residue at the α-sarcin/ricin loop of 28S rRNA. Maize RIP is first produced as a proenzyme with a 25-amino acid internal inactivation region on the protein surface. During germination, proteolytic removal of this internal inactivation region generates the active heterodimeric maize RIP with full N-glycosidase activity. This naturally occurring switch-on mechanism provides an opportunity for targeting the cytotoxin to pathogen-infected cells. Here, we report the addition of HIV-1 protease recognition sequences to the internal inactivation region and the activation of the maize RIP variants by HIV-1 protease in vitro and in HIV-infected cells. Among the variants generated, two were cleaved efficiently by HIV-1 protease. The HIV-1 protease-activated variants showed enhanced N-glycosidase activity in vivo as compared to their un-activated counterparts. They also possessed potent inhibitory effect on p24 antigen production in human T cells infected by two HIV-1 strains. This switch-on strategy for activating the enzymatic activity of maize RIP in target cells provides a platform for combating pathogens with a specific protease.
