BIOCHEMISTRY OF INVERTEBRATE HEMOGLOBINS

血红蛋白在大多数无脊椎动物中广泛但零星分布。 门。大多数这些血红蛋白都有15-17 kDa的链，是 胞内(分子65 kDa)或胞外质量达8000 KDA。一些节肢动物和软体动物具有血红蛋白，其链由 2-20个肌红蛋白样结构域通过多肽键连接。许多人 血红蛋白表现出高度协同的O2结合，并受到强烈的影响 由pH值决定。其他的则是不合作的，完全不受pH的影响。一些人 具有独特的功能，如结合硫化物，这是脊椎动物没有的 血红蛋白。组装和亚基间相互作用的模式有 与脊椎动物的血红蛋白完全不同。不平凡的 形式和功能的多样性提供了一个有吸引力的系统，其中 研究基因结构、功能和进化以及蛋白质 结构和功能。我们的目标是了解 部分无脊椎动物血红蛋白的结构和功能，以及 确定某些簇的组织和核苷酸序列 已经确定的珠蛋白基因。这些系统包括巨人， 蚯蚓200亚单位胞外血红蛋白 软体动物Barbatia和Barbatia的多亚单位、多结构域血红蛋白 Cardita和子囊菌真菌耐人寻味的黄色素和 产氢细菌，产碱杆菌。我们试图确定7个成员如何 蚯蚓血红蛋白链聚集形成高度协同的200 亚基分子，以及协同的O2-结合是如何被 变构调节剂，钙和质子。我们会学到的，就像大多数人一样 不太可能，Cardita珠蛋白的18个结构域是否由唯一的 RNA处理事件。如果结构域珠蛋白的基因显示出预期的 重复的结构，那么差异应该表明一种模式 复制。现有数据表明，这18个领域不仅非常 相似，但它们之间没有显著的氨基酸间隔区。这个 基因结构应该允许评估不平等的可能作用 互换和基因转化。植物的豆状血红蛋白基因有 与脊椎动物珠蛋白基因的3个内含子和4个外显子形成对比 只有2个内含子。目前唯一已确定的无脊椎动物珠蛋白基因是 缺乏内含子和珠蛋白基因的昆虫幼虫摇蚊的基因 来自蚯蚓的内含子/外显子组织是 与脊椎动物的珠蛋白基因相同。这个 真菌和细菌的黄色素可能是进化的纽带 在细胞色素和血红蛋白之间。我们希望，通过确定这些结构 选择低等无脊椎动物的珠蛋白基因，以确定其程度 外显子/内含子组织的变异，并发展出更好的 对珠蛋白进化的理解。

Hemoglobins are widely but sporadically distributed in most invertebrate phyla. Most of these hemoglobins have 15-17 kDa chains and are either intracellular (molecules < 65 kDa) or extracellular with masses to 8000 kDa. Some arthropods and molluscs have hemoglobins with chains composed of 2 to 20 myoglobin-like domains joined by peptide bonds. Many of the hemoglobins exhibit highly cooperative O2 binding and are strongly affected by pH. Others are non-cooperative and completely independent of pH. Some have unique functions such as sulfide binding not shared by vertebrate hemoglobins. The modes of assembly and inter-subunit interaction are totally different from those of vertebrate hemoglobins. The extraordinary diversity of both form and function provides an attractive system in which to investigate gene structure, function and evolution as well as protein structure and function. The goal is to understand the relationship between structure and function in selected invertebrate hemoglobins, and to determine the organization and nucleotide sequences of certain clusters of globin genes that have been identified. These systems include the giant, 200-subunit extracellular hemoglobins of the earthworm, Lumbricus, the multi-subunit, multidomain hemoglobins of the molluscs, Barbatia and Cardita and the intriguing flavohemoglobins of ascomycetous fungi and the hydrogen bacterium, Alcaligenes. We seek to determine how the 7 constituent chains of Lumbricus hemoglobin assemble to form a highly cooperative 200 subunit molecule, and how the cooperative O2-binding is modulated by the allosteric modulators, calcium and protons. We will learn, as seems most unlikely, whether the 18 domains of Cardita globin arose by unique RNA-processing events. If the genes of the domain globins show the expected repeating structures, then the differences should indicate a pattern of duplication. Existing data indicate not only that the 18 domains are very similar, but that no significant amino acid spacers occur between them. The gene structure should allow assessment of the possible roles of unequal crossing-over and gene conversion. The leghemoglobin genes of plants have 3 introns and 4 exons in contrast to the genes for vertebrate globins which have only 2 introns. The only invertebrate globin genes now determined are those of the insect larva Chironomus which lacks introns, and a globin gene from the earthworm Lumbricus, the intron/exon organization of which is identical with that of the globin genes of vertebrates. The flavohemoglobins of fungi and bacteria may provide an evolutionary link between cytochromes and hemoglobins. We hope, by determing the structures of selected globin genes of lower invertebrates, to determine the extent of variation of the exon/intron organization and to develop a better understanding of globin evolution.