Researchers find evidence of a ‘hidden state’ involving one of Earth’s most abundant ions – Zoo House News
In an otherwise straightforward study of the mechanism of assembly of calcium phosphate clusters, researchers from UC Santa Barbara and New York University (NYU) made a surprising discovery: phosphate ions in water have a curious habit of spontaneously switching between their commonly encountered hydrated state and a mysterious, previously unreported “dark” condition. This recently discovered behavior, they say, has implications for understanding the role of phosphate species in biocatalysis, cellular energy balance, and the formation of biomaterials. Their findings are published in the Proceedings of the National Academy of Sciences.
“Phosphate is everywhere,” said UCSB chemistry professor Songi Han, one of the authors of an article in the Proceedings of the National Academy of Sciences. The ion consists of a phosphorus atom surrounded by four oxygen atoms. “It’s in our blood and in our serum,” Han continued. “It’s in every biologist’s buffer, it’s on our DNA and RNA.” It’s also a structural component of our bones and cell membranes, she added.
Bound to calcium, phosphates form small, molecular clumps on their way to form mineral deposits in cells and bones. That’s what Han and his collaborators Matthew Helgeson at UCSB and Alexei Yerschow at NYU wanted to study and characterize, hoping to uncover quantum behavior in symmetric phosphate clusters proposed by UCSB physics professor Matthew Fisher. But first, the researchers had to set up control experiments that included scans of phosphate ions in the absence of calcium by nuclear magnetic resonance spectroscopy (NMR) and cryogenic transmission electron microscopy (cryo-TEM).
Because the project’s UCSB and NYU students collected reference data involving the naturally occurring isotope phosphorus 31 in aqueous solutions at different concentrations and temperatures, their results fell short of expectations. For example, Han said, the line that depicts the spectrum for 31P during NMR scans is said to narrow with increasing temperatures.
“The reason is that the molecules tumble faster at higher temperatures,” she explained. Typically, this rapid molecular motion would balance out the anisotropic interactions or interactions dependent on the relative orientations of these small molecules. The result would be a narrowing of the resonances measured by the NMR instrument.
“We expected a simple phosphorus NMR signal with a peak that narrows at higher temperatures,” she said. “Surprisingly, however, we measured spectra that broadened and caused the complete opposite of what we expected.”
This conflicting result set the team on a new path and followed experiment after experiment to determine the cause at the molecular level. The conclusion after a year of eliminating one hypothesis after the other? Phosphate ions formed clusters under a variety of biological conditions—clusters that eluded direct spectroscopic detection and were therefore probably never observed before. In addition, the measurements indicated that these ions were alternating between a visible “free” state and a dark “composite” state, hence the broadening of the signal instead of a sharp peak.
In addition, the number of these composite states also increased with increasing temperature, another temperature-dependent behavior, according to co-lead author Mesopotamia Nowotarski.
“The conclusion from these experiments was that the phosphates can dehydrate and thus move closer together,” she said. At lower temperatures, the vast majority of these phosphates in solution are attached to water molecules that form a protective water mantle around them. This hydrated state is typically assumed when considering how phosphate behaves in biological systems. But at higher temperatures, Nowotarski explained, they shed their water shields so they stick to each other. This concept was confirmed by NMR experiments probing the phosphate-water envelope and further validated by analysis of cryo-TEM images to identify the presence of clusters and modeling of the energetics of phosphate assembly by co-lead author Joshua dust
According to the researchers, these dynamic phosphate arrangements and hydration shells have important implications for biology and biochemistry. Phosphate, said chemical engineer Matthew Helgeson, is a commonly understood “currency” used in biological systems to store and use energy by converting it into adenosine triphosphate (ATP) and adenosine diphosphate (ADP). “If hydrated phosphate, ADP, and ATP represent small ‘bills’, this new discovery suggests that these smaller currencies can be exchanged for much larger denominations — say, $100 — that may have very different interactions with biochemical processes than they currently do.” known mechanisms. ” he said.
In addition, many biomolecular components contain phosphate groups that can similarly form clusters. Therefore, finding that these phosphates can assemble spontaneously could shed some light on other fundamental biological processes such as biomineralization – how shells and skeletons form, as well as protein interactions.
“We also tested a range of phosphates, including those incorporated into the ATP molecule, and they all seem to show the same phenomenon, and we achieved quantitative analysis for these assemblies,” said co-lead author Jiaqi Lu .
This once-overlooked process could also be important in the areas of cell signaling, metabolism, and disease processes such as Alzheimer’s disease, where attachment of a phosphate group or phosphorylation to the protein tau in our brain is commonly found in neurofibrillary tangles – a hallmark of neurodegeneration. Having seen and studied this assembly behavior, the team is now digging deeper, with studies of the effect of pH on phosphate assembly, genetic translation and assembly of modified proteins, as well as their original work on calcium phosphate assembly.
“It’s really changing the way we think about the role of phosphate groups, which we don’t typically think of as drivers of molecular assembly,” Han said.
The research in this article was also conducted by Tanvi Sheth and Sally Jiao at UC Santa Barbara.