Reconstruction of a probable ancestral form of conger eel galectins revealed their rapid adaptive evolution process for specific carbohydrate recognition
Reconstruction of a probable ancestral form of conger eel galectins revealed their rapid adaptive evolution process for specific carbohydrate recognition
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DOI：
10.1093/molbev/msm185
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发表时间：
2007-11-01
影响因子：
10.7
通讯作者：
Muramoto, Koji
中科院分区：
文献类型：
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作者：
Konno, Ayumu;Ogawa, Tomohisa;Muramoto, Koji
最近，在有毒和生物防御蛋白的各种基因中发现了许多快速适应性进化的例子，其特征是非同义替换对同义替换的替换率较高，包括海鳗半乳糖凝集素、海鳗蛋白I和II（ConI和ConII）。为了了解康姜蛋白的进化过程，我们准备了一个可能的祖先形式Con-anc，对应于系统发育树中ConI和ConII分歧处的推定氨基酸序列，与当前蛋白质分别具有76%和61%的序列同一性。 Con-anc 和 ConII 具有相当的热稳定性和相似的碳水化合物特异性，而 ConI 具有更高的热稳定性并表现出不同的碳水化合物特异性。 Con-anc 对具有 α2,3-唾液酸半乳糖部分的寡糖的特异性降低。这些表明ConI和ConII在显着的选择压力下通过加速进化而进化，以分别提高热稳定性并获得与病原菌中存在的α2,3-唾液酸半乳糖结合的活性。此外，Con-anc和康姜蛋白的比较诱变分析揭示了ConII特异性识别α2,3-唾液酸半乳糖部分的结构基础，以及ConI分别与包括乳-N-二糖基（Gal beta 1-3GlcNAc）或乳糖-N-新二糖基（Gal beta 1-4GlcNAc）残基在内的寡糖的强结合能力。因此，这里提出的使用可能的祖先形式的蛋白质工程是一种强大的方法，不仅可以确定进化过程，而且可以研究蛋白质的结构-活性关系。
Recently, many cases of rapid adaptive evolution, which is characterized by the higher substitution rates of nonsynonymous substitutions to synonymous ones, have been identified in the various genes of venomous and biodefense proteins, including the conger eel galectins, congerins I and II (ConI and ConII). To understand the evolutionary process of congerins, we prepared a probable ancestral form, Con-anc, corresponding to the putative amino acid sequence at the divergence of ConI and ConII in phylogenetic tree with 76% and 61% sequence identities to the current proteins, respectively. Con-anc and ConII had comparable thermostability and similar carbohydrate specificities in general, whereas ConI was more thermostable and showed different carbohydrate specificities. Con-anc showed decreased specificity to oligosaccharides with alpha 2,3-sialyl galactose moieties. These suggest that ConI and ConII have evolved via accelerated evolution under significant selective pressure to increase the thermostability and to acquire the activity to bind to alpha 2,3-sialyl galactose present in pathogenic bacteria, respectively. Furthermore, comparative mutagenesis analyses of Con-anc and congerins revealed the structural basis for specific recognition of ConII to alpha 2,3-sialyl galactose moiety, and strong binding ability of ConI to oligosaccharides including lacto-N-biosyl (Gal beta 1-3GlcNAc) or lacto-N-neobiosyl (Gal beta 1-4GlcNAc) residues, respectively. Thus, protein engineering using a probable ancestral form presented here is a powerful approach not only to determine the evolutionary process but also to investigate the structure-activity relationships of proteins.