Department of Biochemistry, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
Faculty of Agriculture and Biology, Warsaw University of Life Sciences, Warsaw, Poland.
PLoS One. 2014 Jan 16;9(1):e85428. doi: 10.1371/journal.pone.0085428. eCollection 2014.
Annexins are Ca(2+)-binding, membrane-interacting proteins, widespread among eukaryotes, consisting usually of four structurally similar repeated domains. It is accepted that vertebrate annexins derive from a double genome duplication event. It has been postulated that a single domain annexin, if found, might represent a molecule related to the hypothetical ancestral annexin. The recent discovery of a single-domain annexin in a bacterium, Cytophaga hutchinsonii, apparently confirmed this hypothesis. Here, we present a more complex picture. Using remote sequence similarity detection tools, a survey of bacterial genomes was performed in search of annexin-like proteins. In total, we identified about thirty annexin homologues, including single-domain and multi-domain annexins, in seventeen bacterial species. The thorough search yielded, besides the known annexin homologue from C. hutchinsonii, homologues from the Bacteroidetes/Chlorobi phylum, from Gemmatimonadetes, from beta- and delta-Proteobacteria, and from Actinobacteria. The sequences of bacterial annexins exhibited remote but statistically significant similarity to sequence profiles built of the eukaryotic ones. Some bacterial annexins are equipped with additional, different domains, for example those characteristic for toxins. The variation in bacterial annexin sequences, much wider than that observed in eukaryotes, and different domain architectures suggest that annexins found in bacteria may actually descend from an ancestral bacterial annexin, from which eukaryotic annexins also originate. The hypothesis of an ancient origin of bacterial annexins has to be reconciled with the fact that remarkably few bacterial strains possess annexin genes compared to the thousands of known bacterial genomes and with the patchy, anomalous phylogenetic distribution of bacterial annexins. Thus, a massive annexin gene loss in several bacterial lineages or very divergent evolution would appear a likely explanation. Alternative evolutionary scenarios, involving horizontal gene transfer between bacteria and protozoan eukaryotes, in either direction, appear much less likely. Altogether, current evidence does not allow unequivocal judgement as to the origin of bacterial annexins.
钙黏蛋白是一种与 Ca(2+) 结合的膜结合蛋白，在真核生物中广泛存在，通常由四个结构相似的重复结构域组成。人们普遍认为脊椎动物钙黏蛋白源自双重基因组复制事件。有人假设，如果发现单个结构域钙黏蛋白，它可能代表与假设的原始钙黏蛋白相关的分子。最近在一种名为 Cytophaga hutchinsonii 的细菌中发现了一种单结构域钙黏蛋白，这显然证实了这一假说。然而，这里我们呈现出一个更为复杂的情况。我们使用远程序列相似性检测工具，对细菌基因组进行了调查，以寻找钙黏蛋白样蛋白。总共在 17 种细菌物种中鉴定出约 30 种钙黏蛋白同源物，包括单结构域和多结构域钙黏蛋白。彻底的搜索除了在 Cytophaga hutchinsonii 中发现已知的钙黏蛋白同源物外，还在拟杆菌门/绿菌门、芽单胞菌门、β-和 δ-变形菌门以及放线菌门中发现了同源物。细菌钙黏蛋白的序列与基于真核生物构建的序列图谱具有远程但具有统计学意义的相似性。一些细菌钙黏蛋白具有额外的不同结构域，例如那些特征性的毒素结构域。细菌钙黏蛋白序列的变化比真核生物中的变化更为广泛，并且结构域结构不同，这表明在细菌中发现的钙黏蛋白实际上可能源自原始细菌钙黏蛋白，而真核钙黏蛋白也是由此衍生而来的。细菌钙黏蛋白起源于古老的假说必须与以下事实相协调：与已知的数千种细菌基因组相比，具有钙黏蛋白基因的细菌菌株数量显著较少，并且细菌钙黏蛋白的系统发育分布也异常分散。因此，在几个细菌谱系中发生大量钙黏蛋白基因丢失或非常不同的进化似乎是一个可能的解释。涉及细菌和原生动物真核生物之间的水平基因转移的替代进化情景，无论方向如何，似乎不太可能。总之，目前的证据尚不能明确判断细菌钙黏蛋白的起源。
