Shaw A, Fortes P A, Stout C D, Vacquier V D
Department of Molecular Biology, Scripps Research Institute, La Jolla, California 92037-1093, USA.
J Cell Biol. 1995 Sep;130(5):1117-25. doi: 10.1083/jcb.130.5.1117.
Lysin is a 16-kD acrosomal protein used by abalone spermatozoa to create a hole in the egg vitelline envelope (VE) by a nonenzymatic mechanism. The crystal structure of the lysin monomer is known at 1.9 A resolution. The surface of the molecule reveals two tracks of basic residues running the length of one surface of the molecule and a patch of solvent-exposed hydrophobic residues on the opposite surface. Here we report that lysin dimerizes via interaction of the hydrophobic patches of monomers. Triton X-100 dissociates the dimer. The crystal structure of the dimer is described at 2.75 A resolution. Fluorescence energy transfer experiments show that the dimer has an approximate KD of 1 microM and that monomers exchange rapidly between dimers. Addition of isolated egg VE dissociates dimers, implicating monomers as the active species in the dissolution reaction. This work represents the first step in the elucidation of the mechanism by which lysin enables abalone spermatozoa to create a hole in the egg envelope during fertilization.
溶素是一种16千道尔顿的顶体蛋白，鲍鱼精子利用它通过非酶机制在卵黄膜（VE）上制造一个孔。溶素单体的晶体结构已知，分辨率为1.9埃。分子表面显示出两条碱性残基链沿着分子一个表面的长度延伸，以及在相对表面上有一片暴露于溶剂的疏水残基。在此我们报告，溶素通过单体的疏水区域相互作用形成二聚体。Triton X-100可使二聚体解离。二聚体的晶体结构在分辨率为2.75埃时得到描述。荧光能量转移实验表明，二聚体的解离常数约为1微摩尔，且单体在二聚体之间快速交换。添加分离的卵黄膜会使二聚体解离，这表明单体是溶解反应中的活性物质。这项工作是阐明溶素在受精过程中使鲍鱼精子在卵膜上制造孔的机制的第一步。
