Recombinant Expression, Purification, and In Silico Structural Discovery of a Non-TRP-family 5-Hydroxyisourate Hydrolase from Lactiplantibacillus plantarum L123
This study reports the first identification, purification, and structural characterization of a non-TRP-family 5-hydroxyisourate hydrolase from *Lactiplantibacillus plantarum* L123, revealing a distinct all-α-helical fold with a putative His-Glu-His catalytic triad that expands the known diversity of uric acid catabolism enzymes.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Imagine your body is a bustling city, and like any city, it produces waste. Usually, this trash is broken down and recycled efficiently. But sometimes, the city's waste management system glitches, and a specific type of garbage called "uric acid" starts piling up. When this happens, it can cause a painful condition known as hyperuricemia, where sharp crystals form in your joints. For a long time, scientists thought the only way to fix this was to stop the trash from being made in the first place or to help the body flush it out. However, a new frontier in science is looking at tiny, friendly bacteria—probiotics—that might act like a specialized cleanup crew, actually eating the uric acid before it causes trouble.
To understand how these bacteria might work, we need to look at the assembly line of waste disposal. First, an enzyme called "uricase" turns uric acid into a messy, unstable intermediate called 5-hydroxyisourate (HIU). If left alone, HIU is like a ticking time bomb; it falls apart on its own and creates harmful sparks (reactive oxygen species) that can damage the city. To prevent this disaster, a second enzyme, 5-hydroxyisourate hydrolase (HIUHase), rushes in to quickly break HIU down into something harmless. Until now, scientists knew that most living things use a very specific, well-known type of HIUHase that looks like a four-piece puzzle made of a certain shape (the TRP family). But what if there was a different kind of cleanup crew hiding in the bacteria we eat? That is the mystery this paper sets out to solve.
The researchers in this study decided to investigate a specific probiotic bacterium called Lactiplantibacillus plantarum L123. They suspected this microbe had a secret weapon: a gene (named orf02481) that might code for a unique HIUHase. To test this, they didn't just guess; they built a factory inside a common lab bacterium (E. coli) to mass-produce this specific protein. They successfully purified the enzyme, resulting in a very clean sample that weighed about 45 kDa (a unit of molecular weight) and was over 95% pure. When they tested it, the enzyme worked! It successfully broke down the unstable HIU, showing a specific activity of 30.01 ± 4.90 mU/mg. While this isn't as fast as the enzymes found in soybeans (which are around 10 U/mg), it proved that this bacterium definitely possesses a functional HIUHase.
The real magic, however, happened when the scientists looked at the enzyme's blueprint using computer simulations. They expected to find the familiar four-piece TRP puzzle that everyone else had. Instead, they found something completely different. The paper reveals that this new enzyme does not belong to the TRP family at all. It lacks the usual genetic markers and, according to computer models (AlphaFold2), it folds into a shape made almost entirely of spirals (alpha-helices), looking nothing like the flat, sheet-like structures of the known enzymes.
Even more surprising was the discovery of how this new enzyme works. The standard TRP enzymes use a team of three helpers (a catalytic triad) consisting of two Histidines and one Arginine to do their job. This new enzyme, however, uses a different trio: two Histidines and one Glutamate. The computer models suggest this team works in a unique way, using a different set of tools to grab and break down the waste. The study concludes that this is the first time a HIUHase has been purified from a lactic acid bacterium, and it belongs to a completely new structural family (PF02517) that scientists hadn't realized could perform this specific task. It's like discovering a new species of bird that flies using a completely different wing shape than any other bird we've ever seen, proving that nature has more than one way to solve the problem of waste disposal.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.