报告题目：Structure of Origin Recognition Complex Bound to Autonomously Replicating Sequence
报告人：高 宁 教授
主持人：何向伟 教授
时 间：2018年4月19日（周四）下午4点
地 点：纳米楼457报告厅
报告人简介：
高宁博士现为北京大学生命科学学院长聘教授，北京大学-清华大学联合生命中心研究员。
高宁教授于2000年获北京大学学士学位、2006年获纽约州立大学奥尔巴尼分校生物医学系博士学位。2006-2008年先后在纽约沃兹沃斯中心（Wadsworth Center）、霍华德休斯医学研究所、哥伦比亚大学生化和分子生物物理系从事博士后研究。
高教授已获得国家自然基金委杰出青年基金资助、国家自然科学基金委优秀青年基金资助，荣获北京大学�方基金、谈家桢生命科学奖、茅以升北京青年科技奖、中源协和生命医学创新突破奖等荣誉。现任中国电子显微镜学会低温电镜专业委员会委员、中国生物物理学会单分子生物学分会理事、中国生物物理学会冷冻电镜分会副理事长兼秘书长。
高教授主要致力于阐明细胞内大型蛋白-核酸复合物形成的分子机器的精细结构及工作分子机制，近年来的科研工作着重于核糖体的生物生成（ribosome biogenesis）、蛋白质生物合成的调控、DNA复制起始调控等重要基础生物学过程。实验室主要采用冷冻电镜三维重构的方法分析大型复合物的高分辨结构，辅助遗传学、细胞生物学、生化分子生物学手段回答大分子机器在功能执行过程中的机制性问题。同时，针对结构课题中的技术难点，实验室还致力于冷冻电镜方法学的研究，包括样品制备技术和算法的改进等。至今已在Cell、Nature、Cell Research、Molecular Cell等国际知名期刊发表多篇研究论文。
讲座摘要：
The Origin Recognition Complex (ORC) consists of six highly conserved subunits, Orc1-6.Despite the conservation in protein sequence, ORC from different species have divergent DNA binding specificities ranging from an absolute requirement for a specific sequence in Saccharomyces cerevisiae to no known sequence requirement in humans.Yet ORC of all species bind DNA to mark the site for DNA replication initiation. Here, we report a 3-A cryo-EM structure of S.cerevisiae ORC bound to a 72-bp origin DNA containing the ARS consensus sequence (ACS) and B1 element ORC encircles DNA through extensive interactions with both phosphate backbone and bases, and bends DNA at the ACS and B1 sites.A key structural feature is that a conserved basic amino acid patch of Orc1 inserts deeply into the minor groove of the ACS for specific base recognition. In addition, a species-specific helical insertion located in the winged-helix domain of Orc4 is embedded in the major groove of the ACS through hydrophobic interactions with a stretch of conserved thymines.Importantly, these base-specific contacts at the ACS are mostly with invariant bases.Moreover, similar major and minor-groove insertions are also embedded in the B1 site by basic patch motifs from Orc2 and Orc5, respectively, to contact bases and to bend DNA. Our findings show that yeast ORC binds thymine-rich DNA in a universally conserved mechanism mainly via the Orc1 basic patch element but acquires its species-specific sequence recognition from the divergent Orc4 insertion helix. This work pinpoints a conserved role of ORC in modulating DNA structure to facilitate origin selection and helicase loading in all eukaryotes.
