AI Unveils Crucial Protein Complex in Sperm-Egg Fertilization

How life begins: Egg, sperm, and a covert team of proteins - Earth.com

Ever wonder about how life starts? Most of us know it has something to do with eggs, sperm, and maybe proteins, but the exact choreography that sees these partners meet and merge has remained somewhat of an enigma. This fascinating tale is far from over, as researchers utilizing Google's spectacular AlphaFold technology discovered a surprising new twist. Typically, opposites attract. In this context, you cannot find a pair more diverse than the egg and the sperm. One is a microscopic champion swimmer, always on the go, while the other is a stationary, voluminous entity, the blueprint for life. Their union forms the bedrock of sexual reproduction, spanning across every species on planet Earth. The "how" behind this vital fusion has always remained shrouded in mystery, until now. A breakthrough study enlightens us; an interlocked trio of proteins opens the doors to this bond, making the sperm and egg recognize and stick together. Evidently, this threesome protein bundle is a shared heritage across species - from fish to mammals, and most definitely humans too. Picture life's opening scene - a sperm navigating its way to an awaiting egg. The sperm and egg then create a bond, recognizing each other almost instantly. Within fractions of a second, the head of the sperm plunges into the egg, like stepping through an open doorway. This fusion brings to life a zygote, the starting point of a new creature. Past studies had identified four "star" proteins on the sperm - with memberships in both mammalian and fish sperm clubs - that are crucial for fertilization. Yet, the exact nature of their teamwork and their modus operandi remained elusive. Taking up this challenge, Andrea Pauli, a renowned molecular and developmental biologist at the Research Institute of Molecular Pathology (IMP) in Vienna, alongside her brilliant team, questioned how these sperm proteins might collaborate during the crucial fertilization process. For this mission, they enlisted the prowess of AlphaFold, an artificial intelligence tech prodigy that bagged the Nobel Prize in Chemistry. AlphaFold can predict the shape of a protein, an essential attribute when dealing with cellular functions. Armed with this AI, the researchers compared the four sperm proteins common to mammals and fish to about 1,400 other proteins on the zebrafish's testes' cell surfaces. They were hoping to find potential allies. "We wanted to find something that we knew would be at the right place and at the right time," said Victoria Deneke, a postdoctoral researcher in Dr. Pauli's lab. It took weeks of analyzing and crunching data to finally predict which proteins might form this super team. The results were remarkable. AlphaFold proposed two of the original proteins would bind with each other and a third, previously unknown protein. The trio, together, would form the team they were looking for. Subsequent testing confirmed AlphaFold's prediction. In both zebrafishes and mice missing the newfound third protein, the males were infertile. Their sperm, even though mobile, couldn't fuse with an egg without the protein. Further evidence revealed that this trio of sperm proteins worked as a unit in both zebrafish and humans. Think of the trio of proteins as a "key" that opens a "lock" on the egg cell. For fish, this lock is a protein appropriately named 'Bouncer.' Without the Bouncer protein, the sperm cannot gain entry into the egg. Interestingly, though, the mammalian lock in this story is not Bouncer; it's an unrelated protein named Juno. This suggests that at some point in our evolutionary journey, different egg proteins evolved to bind with the sperm protein bundle. The mystery that baffles Dr. Pauli's team is how the lock changed while the key on the sperm remained the same. Amber Krauchunas, a reproductive biologist at the University of Delaware, views this research as exciting and a big step forward. Earlier in the year, another research group independently used AlphaFold, and they predicted the existence of the same three-protein bundle in mammals. The fact that two groups arrived at the same conclusion significantly boosts confidence in the findings. Yet, the curtain hasn't completely lifted on the mystery of egg, sperm, protein and eventual fertilization. Some sperm proteins, known to be common across mammals and fish, are not part of this trio. It raises the question - what roles do they play? "This is such a fundamental question with so few molecular answers," Dr. Pauli said. "It's amazing." For now, we can relish the fact that we are a bit closer to understanding one of life's greatest mysteries. Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Sperm Can't Unlock an Egg Without This Ancient Molecular Key

Using Google's AlphaFold, researchers identified the bundle of three sperm proteins that seem to make sexual reproduction possible. They're the original odd couple: One is massive, spherical and unmoving. The other is tiny, has a tail and never stops swimming. Yet the union of egg and sperm is critical for every sexually reproducing animal on Earth. Exactly how that union occurs has long been a mystery to scientists. A study published Thursday in the journal Cell that relied on Nobel Prize-honored artificial intelligence technology shows that an interlocked bundle of three proteins is the key that lets sperm and egg bind together. That crucial bundle is shared by animals as distantly related as fish and mammals, and most likely including humans. For nearly all animals on Earth, life begins with a sperm cell making its way to an egg's cell membrane. Somehow, the two cells recognize each other and bind together. Then, in a flash, the sperm head passes into the egg, as if stepping through a door. Now the fused cell is a zygote and ready to grow into a new animal. In earlier research, scientists had found four proteins on mammal sperm that are also present on fish sperm and are needed for fertilization. But no one knew whether they might work as a team to enter an egg, or how. In the new study, Andrea Pauli, a molecular and developmental biologist at the Research Institute of Molecular Pathology in Vienna, and collaborators across several institutions asked how sperm proteins might team up during fertilization. The researchers relied on AlphaFold, a technology that shared the Nobel Prize in Chemistry last week. It uses A.I. to predict the shape of a protein. With AlphaFold, the team could compare the four sperm proteins shared across mammals and fish against a library of about 1,400 other proteins found on cell surfaces in zebrafish testes, looking for potential partners. "We wanted to find something that we knew would be at the right place and at the right time," said Victoria Deneke, a postdoctoral researcher in Dr. Pauli's lab. Even for AlphaFold, this was a challenge. "It was running for two or three weeks," Dr. Deneke said, monopolizing the campus's computing resources. "Other people at the institute were not so happy," Dr. Pauli added. Finally, AlphaFold predicted that two of the original shared sperm proteins would bind to each other, along with a third protein that was previously unknown, creating a team of three. Lab experiments confirmed the program's guess: Male zebrafish missing the newly discovered third protein were infertile, as were male mice. Their sperm swam normally but couldn't fuse with an egg. The scientists also found biochemical evidence that the three sperm proteins were working as a unit, both in zebrafish and humans. It's likely that the same crucial bundle exists in many -- or all -- animals with a backbone animals, Dr. Pauli said. She described the sperm protein bundle as a kind of key, which fits with a lock on an egg cell. In fish, that lock is a protein named Bouncer -- appropriately, as the sperm head can't enter the egg without it. Earlier research also identified a lock molecule in mammal eggs, which binds to one of the proteins in the three-protein bundle. Oddly, though, the mammalian lock isn't Bouncer. It's an unrelated protein called Juno. That means somewhere in history, animals must have evolved different egg proteins to bind the sperm protein bundle. That presents a mystery, Dr. Pauli said: The lock has changed, yet somehow, "the key on the sperm stayed the same." "We would love to know the answer," she added. Amber Krauchunas, a reproductive biologist at the University of Delaware who was not involved in the new research, called the new paper "really exciting." Earlier this year, a different research group independently used AlphaFold and predicted the existence of the same three-protein bundle in mammals. "The fact that two independent groups came to the same conclusions certainly increases our confidence in the results," Dr. Krauchunas said. Even so, she said, "more work certainly remains to uncover the mysteries of fertilization." For example, some sperm proteins are known to be shared across mammals and fish but aren't part of this bundle; what are they doing? "This is such a fundamental question with so few molecular answers," Dr. Pauli said. "It's amazing."

AI reveals how sperm sticks to egg during fertilization

Two studies identify elusive protein complex with help from software developed by some of this year's Nobel winners The microscopic union of sperm and egg might be life's most fundamental encounter, but there's a lot science doesn't know about what happens at this crucial moment. In particular, researchers have struggled to pin down the molecular machinery that orchestrates how the two cells stick together, fuse, and share genetic material. Two teams shine new light on the key first step of this process with the aid of AlphaFold, the artificial intelligence-powered technology that earned Google DeepMind researchers a share of the Nobel Prize in Chemistry earlier this month. Guided by its predictions, both have independently identified a complex of three proteins that sits on the head of a sperm and locks onto the surface of an egg cell during fertilization. The findings, published in today and in in April, span zebrafish, mouse, and human proteins. Combined, they suggest a high level of conservation in how sperm stick to eggs across vertebrates and confirm suspicions that the interactions of multiple proteins are required, says Rutgers University's Andrew Singson, who was not involved in either study. The results also showcase the potential of AI to resolve problems that have long confounded scientists, especially for fields such as reproductive biology where experiments with human tissue might be unethical, says Gavin Wright, a biochemist at the University of York and co-author on the paper. "Mixing human sperm and egg in a dish is quite rightly tightly regulated," he says. In these scenarios, "it might be that using computational modeling is really the only way." Researchers had previously discovered a number of individual proteins involved in vertebrate fertilization. In 2005, a team in Japan showed that deleting a particular gene in mice caused the animals to make healthy-looking, motile sperm that nevertheless failed to fuse with egg cells. They named the gene Izumo1, after a Shinto shrine to marriage. Nearly a decade later, another group discovered a protein receptor on egg cells that bound to Izumo1, and named it Juno, after the Roman goddess of fertility. Others have found additional proteins: in 2020, for example, a team showed that mice that had had their Spaca6 gene knocked out produced sperm with the same defects as rodents lacking Izumo1. Although signs pointed to the two sperm proteins and the egg receptor needing to interact to join the cells, the details remained elusive. So the two groups behind the new studies independently turned to the recently developed Multimer tool of AlphaFold, which analyzes how different proteins could slot together based on their structures. In both teams' studies, the AI program predicted the formation of a three-protein complex, or trimer, on sperm between Izumo1, Spaca6, and another known protein, Tmem81, which had not previously been associated with fertilization. In the study, the team including Wright and led by structural biologist Luca Jovine at the Karolinska Institute analyzed mouse and human protein structures with the program and found the trimer could form a larger complex with Juno and another protein on egg cells called CD9. The other team, led by molecular biologist Andrea Pauli at the Research Institute of Molecular Pathology (IMP), went further and carried out experiments to see whether their AI-identified complex existed in the real world. They found that deleting the gene for Tmem81 in zebrafish and mice caused the same sperm defects as did deletions of Izumo1 or Spaca6, confirming this third protein was also critical for fertilization. The researchers also found that adding antibodies for Izumo1, Spaca6, or Tmem81 to samples of zebrafish sperm always pulled out all three proteins together, confirming they formed a trimer, as AI had predicted. "I think that was probably one of the happiest days in lab," says Victoria Deneke, an IMP molecular biologist and co-author of the paper. "It's not a prediction, ... it's actual experimental data." Surprisingly, AlphaFold-Multimer also predicted -- and experiments with zebrafish proteins subsequently supported -- that different parts of this sperm trimer are responsible for binding to the distinctive receptors of mammalian versus zebrafish eggs. It's remarkable that the sperm complex has stayed the same across vertebrate evolution while egg receptors have changed, Pauli says. The findings might reflect how eggs have adapted to such different environments -- fish eggs are typically fertilized outside the animal, while mammalian eggs are fertilized within, she notes. Although Pauli's team identified the sperm trimer in zebrafish and later showed that the three human proteins could bind to one another in a test tube, neither study shows directly that the complex forms naturally on mammalian sperm or that it binds to mammalian eggs, cautions Ahmed Ziyyat, a reproductive biologist at the Cochin Institute and Paris City University. Nevertheless, these basic biology revelations could one day have clinical implications, researchers suggest. "The more proteins we know [about], and the more genes we know that are involved in fertilization, the better we'll be at screening for mutations in patients [with infertility]," says Enrica Bianchi, a co-author on the paper and a reproductive biologist at the University of Rome Tor Vergata. The findings could also aid research on contraception by revealing new ways to block sperm and egg from interacting, notes Christopher Barratt, who leads the reproductive medicine unit at the University of Dundee and was not involved in the work. Pauli says her group is now studying what happens after the sperm and egg lock together, as the trimer alone doesn't seem responsible for fusing the two cells. "That is clearly the Holy Grail, the big question in the field," she says.

AI-powered discovery identifies lock-and-key process in sperm and egg

The researchers employed the artificial intelligence tool AlphaFold to uncover how sperm proteins interact at the molecular level, shedding light on a fundamental aspect of fertilization shared across vertebrates. Fertilization begins when sperm navigate to an egg, guided by chemical signals. Once they reach the egg, sperm bind to the egg's surface, initiating a fusion of their genetic material to form a zygote. However, the precise molecular mechanisms allowing this critical interaction have remained elusive. Andrea Pauli's lab at the Research Institute of Molecular Pathology (IMP) in Vienna, along with international collaborators, utilized AlphaFold Multimer to predict protein interactions that guide sperm-egg fusion. The team focused on sperm membrane proteins, using AlphaFold to predict which proteins might bind together. Their analysis revealed that two previously known proteins, Izumo1 and Spaca6, interact with a third, newly discovered protein: Tmem81. We were surprised to discover a new protein that had never been characterised before," said Andreas Blaha, co-first author of the study. This new trimeric complex -- composed of Izumo1, Spaca6, and Tmem81 -- was shown to play a critical role in fertilization. When this complex was disrupted, male zebrafish and mice became infertile.

AlphaFold reveals how sperm and egg hook up in intimate detail

An artificial-intelligence tool honoured by this year's Nobel prize has revealed intimate details of the molecular meet-cute between sperm and eggs. The AlphaFold program, which predicts protein structures, identified a trio of proteins that team up to work as matchmakers between the gametes. Without them, sexual reproduction might hit a dead end in a wide range of animals, from zebrafish to mammals. The finding, published 17 October in Cell, unravels the previous notion that just two proteins -- one on the egg and one on the sperm -- would be sufficient to ensure fertilisation, says Enrica Bianchi, a reproductive biologist at the University of Rome 'Tor Vergata', who was not involved in the study. "It's not the old concept of having a key and a lock to open the door anymore," she says. "It's more complicated." Despite its critical role in reproduction, the fusion of egg and sperm in vertebrates is a molecular mystery that has proved difficult to crack. The union of the two cells involves proteins that reside in greasy membranes and that are hard to study using standard biochemical methods. The interactions between these proteins are often weak and fleeting, and it is difficult to harvest enough eggs and sperm from some of researchers' favourite laboratory animals, including mice, for extensive experiments. As a result, early studies of reproductive biology often focused on marine invertebrates that release copious quantities of egg and sperm into water. "If you take a textbook off the shelf and look up fertilisation, you'll read all about sea urchins," says Gavin Wright, a biochemist at the University of York, UK, who was not involved in the study. "It's a tricky thing to research." To overcome the supply problem, Andrea Pauli, a molecular biologist at the Research Institute of Molecular Pathology in Vienna and her colleagues, began their work in zebrafish, a vertebrate that also releases its eggs and sperm into the surrounding water. And to bypass the difficulties of working with membrane proteins in the laboratory, the team used AlphaFold to predict interactions between protein s. Two of AlphaFold's developers were awarded the Nobel Prize for chemistry on 9 October. AlphaFold predicted that three sperm proteins work together to form a complex. Two of these proteins were previously known to be important for fertility. Pauli and her colleagues then confirmed that the third is also critical for fertility in both zebrafish and mice, and that the three proteins interact with one another. The team also found that, in zebrafish, the trio creates a place for an egg protein to bind, providing a mechanism by which the two cells could recognize one another. "It's a way to say, 'Sperm, you found an egg' and 'Egg, you found a sperm'," says Andreas Blaha, a biochemist at the Research Institute of Molecular Pathology and co-author of the paper. The findings might one day yield a way to screen people struggling with infertility, to find out whether problems with this complex could be the cause, says Wright. And the results highlight a role for AlphaFold in studying fertilisation, he adds. "We're limited in terms of experiments," he says. "It might be that these modelling studies have an important role to play in the future."