Hemocyanins are giant oxygen transport proteins that freely float within the hemolymph of most molluscs. The basic quaternary structure of molluscan hemocyanins is a cylindrical decamer with a diameter of 35 nm which is built of 400 kDa subunits. Previously published results, however, showed that one out of two hemocyanin subunits of Rapana venosa encompasses two polypeptides, one 300 kDa and one 100 kDa polypeptide which aggregate to typical 4 MDa and 8 MDa hemocyanin (di-)decamer molecules. It was shown that the polypeptides are bound most probably by one or more cysteine disulfide bridges but it remained open if these polypeptides were coded by one or two genes. Our here presented results clearly showed that both polypeptides are coded by one gene only and that this phenomenon can also be found in the gastropod Nucella lapillus. Thus, it can be defined as clade-specific for Muricidae, a group of the very diverse Caenogastropoda. In addition, we discovered a further deviation of this hemocyanin subunit within both species, namely a region of 340 mainly hydrophilic amino acids (especially histidines and aspartic acids) which have not been identified in any other molluscan hemocyanin, yet. Our results indicate that, within the quaternary structure, these additional amino acids most probably protrude within the inner part of didecamer cylinders, forming a large extra mass of up to 800 kDa. They presumably influence the structure of the protein and may affect the functionality. Thus, these findings reveal further insights into the evolution and structures of gastropod hemocyanins.

血蓝蛋白是巨大的氧运输蛋白，可在大多数软体动物的血淋巴中自由漂浮。软体动物血蓝蛋白的基本四级结构是直径为 35 nm 的圆柱形十聚体，由 400 kDa 的亚基组成。然而，先前发表的结果表明， Rapana venosa的两个血蓝蛋白亚基中的一个包含两种多肽，一种 300 kDa 和一种 100 kDa 多肽，它们聚集成典型的 4 MDa 和 8 MDa 血蓝蛋白（二）十聚体分子。结果表明，这些多肽很可能通过一个或多个半胱氨酸二硫键结合，但如果这些多肽由一或两个基因编码，则其保持开放状态。我们在此提出的结果清楚地表明，两种多肽仅由一个基因编码，并且这种现象也可以在腹足动物Nucella lapillus 中发现。因此，它可以被定义为鼠科（一组非常多样化的腹足纲动物）特有的分支。此外，我们发现这两个物种内的血蓝蛋白亚基有进一步的偏差，即由 340 个主要亲水性氨基酸（尤其是组氨酸和天冬氨酸）组成的区域，这些氨基酸尚未在任何其他软体动物血蓝蛋白中发现。我们的结果表明，在四级结构中，这些额外的氨基酸最有可能突出在二十聚体圆柱体的内部，形成高达 800 kDa 的大额外质量。它们可能会影响蛋白质的结构并可能影响其功能。因此，这些发现进一步揭示了腹足动物血蓝蛋白的进化和结构。