Hirohashi Noritaka, Vacquier Victor D
Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0202, USA.
J Biol Chem. 2002 Mar 8;277(10):8041-7. doi: 10.1074/jbc.M110661200. Epub 2002 Jan 2.
Sea urchin egg jelly (EJ) triggers sperm acrosome reaction (AR), an exocytotic event required for membrane fusion of the gametes. Purified fucose sulfate polymer (FSP) in EJ is one inducer of the AR. Binding of FSP to its receptor regulates opening of two distinct calcium channels and also elevates intracellular pH (pH(i)). EJ also contains sialic acid-rich glycans (sialoglycans (SG)) that were isolated by beta-elimination followed by DEAE chromatography. In the presence of limiting amounts of FSP, the SG fraction markedly potentiates the AR; however, by itself SG has no activity. The SG fraction increases the pH(i) of sperm without increasing intracellular Ca(2+). The SG-induced increase in pH(i) is not blocked by nifedipine or high K(+), whereas the FSP-induced pH(i) increase is sensitive to both these agents. Treatment of the SG fraction with neuraminidase or mild metaperiodate that specifically cleaves the glycerol side chain of sialic acid abolishes the AR potentiation and ability of SG to elevate pH(i). These data are the first to show that there are at least two pathways to induce sperm pH(i) increase and that egg surface sialic acid plays a role in triggering the sperm AR.
海胆卵胶（EJ）可触发精子顶体反应（AR），这是配子膜融合所需的一种胞吐事件。EJ中的纯化硫酸岩藻糖聚合物（FSP）是AR的诱导剂之一。FSP与其受体的结合调节两种不同钙通道的开放，并提高细胞内pH值（pH(i)）。EJ还含有富含唾液酸的聚糖（唾液酸聚糖（SG）），通过β-消除法随后进行DEAE色谱法分离得到。在FSP量有限的情况下，SG组分显著增强AR；然而，SG本身没有活性。SG组分可增加精子的pH(i)，而不增加细胞内Ca(2+)。SG诱导的pH(i)升高不受硝苯地平或高钾的阻断，而FSP诱导的pH(i)升高对这两种试剂均敏感。用神经氨酸酶或轻度高碘酸盐处理SG组分，特异性切割唾液酸的甘油侧链，可消除AR增强作用以及SG升高pH(i)的能力。这些数据首次表明，至少有两条途径可诱导精子pH(i)升高，并且卵表面唾液酸在触发精子AR中起作用。
