Directed Evolution of Homing Endonucleases for Human Gene Therapy

描述(申请人提供)：归巢内切酶是催化DNA序列特定双链断裂的酶，并能显著刺激细胞中这些断裂的同源重组。这些酶在基因治疗中的基因纠正或系统生物学、功能基因组学、干细胞工程和代谢工程中的基因改变等方面具有巨大的应用潜力。然而，归巢内切酶的天然靶向序列有限，这严重阻碍了其应用。这项研究的广泛和长期目标是设计能够识别和切割与人类遗传疾病相关的新DNA序列的归巢内切酶，并研究归巢内切酶精致DNA序列特异性的分子决定因素。使用一个特性良好的归巢内切酶I-SCEI作为模型系统，我们将使用组合蛋白质工程策略来产生I-SCEI变异体，该变异体切割在与镰状细胞性贫血相关的突变的血红蛋白β基因中发现的新的靶DNA序列。这种I-SCEI基因工程突变体具有作为治疗镰状细胞性贫血的新型基因治疗药物的巨大潜力。此外，我们将使用各种生化和生物物理方法，在体外和哺乳动物细胞中对选定的I-SCEI工程变体进行表征。这些研究将为归巢内切酶DNA序列特异性的分子基础提供新的见解。同样重要的是，我们预计这一探索性/开发性(R21)项目将为设计用于生物医学研究和人类基因治疗的各种DNA修饰酶建立一个技术平台。

DESCRIPTION (provided by applicant): Homing endonucleases are enzymes that catalyze DNA sequence specific double-strand breaks and can significantly stimulate homologous recombination at these breaks in cells. These enzymes have great potential for applications such as gene correction in gene therapy or gene alteration in systems biology, functional genomics, stem cell engineering, and metabolic engineering. However, homing endonucleases have a limited natural repertoire of target sequences, which severely hampers their applications. The broad and long-term goal of this research is to engineer homing endonucleases that recognize and cleave novel DNA sequences that are linked with human genetic disorders and to investigate the molecular determinants of the exquisite DNA sequence specificity of homing endonucleases. Using a well-characterized homing endonuclease I-SceI as a model system, we will use combinatorial protein engineering strategies to generate I-SceI variants that cleave new target DNA sequences found in a mutant hemoglobin beta gene associated with sickle cell anemia. Such engineered I-SceI mutants hold tremendous potential as novel gene therapy agents for sickle cell anemia. In addition, we will use a variety of biochemical and biophysical methods to characterize select engineered I-SceI variants both in vitro and in mammalian cells. Such studies will provide novel insights into the molecular basis of the homing endonuclease DNA sequence specificity. Equally important, we anticipate that this exploratory/developmental (R21) project will establish a technology platform for engineering a wide variety of DNA-modifying enzymes for biomedical research and human gene therapy.