What is it about?

Phosphates are present in many biological systems, and have previously been thought to behave as simple ions in solution. We show that there also exist clusters of phosphates (and molecular species containing phosphates) in exchange with the individual ions/molecules in aqueous solutions. The population of these clusters is shown to be affected by solution conditions such as temperature and salt, and we propose a mechanism for their formation.

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Why is it important?

Phosphates are key in many biological functions, such as energy production via ATP hydrolysis, in lipid membranes, in decorating proteins in a process known as posttranslational modification and in bone formation, as well as being a commonly used buffer used in labs. They have previously thought to behave as a simple ionic species in these environments, but we show that the ionic form exists in equilibrium of larger liquid-like clusters of many phosphates. Such clusters could have ramifications for the many different processes that involve phosphates, both in biological and laboratory settings.

Perspectives

Phosphate is the most abundant anion in the human body, participating in metabolism and also representing a key constituent as of cell membranes and bones. When bond with calcium, phosphates are hypothesized to form clusters. However, the underlying assembly mechanism of phosphate species are not well understood. To further explore this, we set up control experiments of phosphate ions in the absence of calcium with nuclear magnetic resonance, and we observed unexpected results which did not comply to the theory, suggesting the existence of spectroscopically invisible phosphate assemblies. This study unrevealed the once overlooked process that the phosphate -containing molecules ubiquitously present in the biological milieu can readily form spectroscopically invisible assemblies under a wide range of solution conditions, highlighting a hitherto unreported property of phosphate’s native state in biological solutions.

Jiaqi Lu

For this work, we originally set out to characterize of the nuclear magnetic resonance signal of phosphates, which we expected to be relatively straightforward. After coming across theoretically unexpected results, we began examining phosphate behavior more rigorously and revealed the existence of a hidden clustered phosphate state that had previously alluded detection. In this sense, this work both adds important scientific knowledge to all research concerning phosphate-containing systems, but also shows the importance of critically questioning strange results and the deeper meaning they may contain.

Joshua Straub
University of California Santa Barbara

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This page is a summary of: Phosphates form spectroscopically dark state assemblies in common aqueous solutions, Proceedings of the National Academy of Sciences, December 2022, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2206765120.
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