ELECTRON CRYSTALLOGRAPHY OF ACROSOMAL BUNDLE

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 在未激活的鲎精子中，一束60 μ m长的肌动蛋白丝被scruin交联，弯曲并缠绕在核的底部。受精时，束展开，并在5秒内完全伸展，以支撑一个指状的膜，即顶体突。这种生物弹簧由储存的弹性能量提供动力，不需要马达蛋白或肌动蛋白聚合的作用。我们的9.5磅延伸束的电子低温显微镜结构显示肌动蛋白-scruin亚基的扭曲、倾斜和旋转与“标准”F-肌动蛋白丝相差很大。该偏离似乎与scruin交联剂的包装要求有关。结构组织允许细丝在伸展状态下包装成高度有序和刚性的束，但也表明了在卷曲和伸展状态之间储存和释放能量的机制。 我们目前正在分析纤维束中肌动蛋白丝的结构和组织，scruin的结构，它与肌动蛋白的关系，以及它在纤维束中的包装。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the unactivated Limulus sperm, a 60 ¿m-long bundle of actin filaments crosslinked by scruin is bent and twisted into a coil around the base of the nucleus. At fertilization the bundle uncoils and fully extends in five seconds to support a finger of membrane, the acrosomal process. This biological spring is powered by stored elastic energy and does not require the action of motor proteins or actin polymerization. Our 9.5 ¿ electron cryomicroscopic structure of the extended bundle shows that twist, tilt, and rotation of actin-scruin subunits deviate widely from a "standard" F-actin filament. This deviation appears to be related to the packing requirements of the scruin cross-linkers. The structural organization allows filaments to pack into a highly ordered and rigid bundle in the extended state, but also suggests a mechanism for storing and releasing energy between the coiled and extended states. We are currently analyzing the structure and organization of the actin filament in the bundle, the structure of the scruin, its relationship to the actin, and its packing in the bundle.