The understanding and prediction of the solubility of biomolecules, even of the simplest ones, reflect an open question and unmet need. Short aromatic tripeptides are among the most highly aggregative biomolecules. However, in marked contrast, Ala-Phe-Ala (AFA) was surprisingly found to be non-aggregative and could be solubilized at millimolar concentrations. Here, aiming to uncover the underlying molecular basis of its high solubility, we explore in detail the solubility, aggregation propensity, and atomic-level structure of the tripeptide. We demonstrate an unexpectedly high water solubility of AFA reaching 672 mM, two orders of magnitude higher than reported previously. The single crystal structure reveals an anti-parallel β sheet conformation devoid of any aromatic interactions. This study provides clear mechanistic insight into the structural basis of solubility and suggests a simple and feasible tool for its estimation, bearing implications for design of peptide drugs, peptides materials, and advancement of peptide nanotechnology.

对生物分子（即使是最简单的生物分子）溶解度的理解和预测反映了一个悬而未决的问题和未满足的需求。短芳香族三肽是聚集性最高的生物分子之一。然而，与此形成鲜明对比的是，令人惊讶的是，Ala-Phe-Ala (AFA) 被发现是非聚集的，并且可以在毫摩尔浓度下溶解。在这里，为了揭示其高溶解度的分子基础，我们详细探讨了三肽的溶解度、聚集倾向和原子级结构。我们证明 AFA 的水溶性出人意料地高，达到 672 mM，比之前报道的高两个数量级。单晶结构揭示了没有任何芳香族相互作用的反平行β折叠构象。这项研究为溶解度的结构基础提供了清晰的机制见解，并提出了一种简单可行的估计工具，对肽药物、肽材料的设计和肽纳米技术的进步具有重要意义。