Proteins are relatively easy to synthesize, compared to nucleic acids and it is likely that there existed a stage prior to the RNA world which can be called the protein world. Some of the three-dimensional (3D) peptide structures in these proteins have, we argue, been conserved since then and may constitute the oldest biological relics in existence. We focus on 3D peptide motifs consisting of up to eight or so amino acid residues. The best known of these is the 'nest', a three- to seven-residue protein motif, which has the function of binding anionic atoms or groups of atoms. Ten per cent of amino acids in typical proteins belong to a nest, so it is a common motif. A five-residue nest is found as part of the well-known P-loop that is a recurring feature of many ATP or GTP-binding proteins and it has the function of binding the phosphate part of these ligands. A synthetic hexapeptide, ser-gly-ala-gly-lys-thr, designed to resemble the P-loop, has been shown to bind inorganic phosphate. Another type of nest binds iron-sulfur centres. A range of other simple motifs occur with various intriguing 3D structures; others bind cations or form channels that transport potassium ions; other peptides form catalytically active haem-like or sheet structures with certain transition metals. Amyloid peptides are also discussed. It now seems that the earliest polypeptides were far from being functionless stretches, and had many of the properties, both binding and catalytic, that might be expected to encourage and stabilize simple life forms in the hydrothermal vents of ocean depths.

中文翻译：

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生命起源的蛋白质三维结构。

与核酸相比，蛋白质相对容易合成，并且可能在RNA世界之前存在一个可以称为蛋白质世界的阶段。从那时起，我们认为这些蛋白质中的某些三维（3D）肽结构一直是保守的，可能构成了现存最古老的生物文物。我们专注于由多达八个左右的氨基酸残基组成的3D肽基序。其中最著名的是“巢”，一个三至七个残基的蛋白质基序，具有结合阴离子原子或原子团的功能。典型蛋白质中10％的氨基酸属于巢，因此是常见的基序。发现了五个残基的巢，这是众所周知的P环的一部分，是许多ATP或GTP结合蛋白的重复特征，并且具有结合这些配体的磷酸部分的功能。已显示设计为类似于P环的合成六肽ser-gly-ala-gly-lys-thr与无机磷酸盐结合。另一类巢结合了铁硫中心。各种其他有趣的3D结构也出现了一系列其他简单的图案。其他结合阳离子或形成运输钾离子的通道；其他肽与某些过渡金属形成催化活性的血红素样或片状结构。还讨论了淀粉样肽。现在看来，最早的多肽远非无功能的延伸，而且具有许多特性，包括结合和催化作用，