A review that examines the expansion of the RNA-binding proteome, evaluates evidence for many non-canonical RBPs, and highlights riboregulation as an emerging mechanism by which RNA controls protein function, complexes, and metabolism.
0:19Welcome to Base by Base, the paper cast that brings genomics to you wherever you are. Thanks for listening. And don't forget to follow and rate us in your podcast app. So, I mean, we've always been taught the central dogma as this strict one way street, right?
0:33Right, yeah, the classic model. Yeah, like DNA is the master architect. RNA is just the, you know, passive instruction manual or messenger. And proteins are the heavy lifting workers that actually carry out the biochemistry of the cell.
0:46Exactly. That's day one of biology class. Right. But what if that instruction manual isn't just passively sitting there waiting to be read? What if the manual is actually, I don't know, bossing the workers around?
0:57Which is a wild concept to wrap your head around. It really is. I mean, how could this flip our understanding of everything from how ourselves survive starvation to, well, how we fight off viral infections?
1:08And what really happens when metabolic enzymes, proteins that are supposed to be busy digesting sugars, suddenly moonlight as RNA binding proteins? It completely shatters that one-way street model. We've relied on for decades.
1:21I mean, we are looking at one of the most significant paradigm shifts in modern molecular biology. Wow, okay, so this is huge. Oh, absolutely. And before we dive into the mechanics of how this works, Today we celebrate the work of researchers at the European molecular biology laboratory, or EMBL, and the Center for Genomic Regulation, CRG, who have fundamentally advanced our understanding of the RNA bound protium.
1:45They've introduced us to this entirely new concept called ribo regulation. Ribo regulation. Okay, let's unpack this shift for everyone listening. To appreciate why this new research is turning the field upside down, I guess we have to look at the classical view of RNA protein interactions first.
2:02Right, the baseline. Historically, we knew about roughly 1000 of these so-called classical RNA binding proteins or RVPs in the mailing cells. And their roles made perfect sense within that standard model, right?
2:13Exactly. They splice RNE transcripts, they transport them out of the nucleus. They facilitate translation at the rivosome, standard maintenance stuff. Right. And the defining feature of those classical RVPs is their structure.
2:26They have these highly specialized evolutionarily conserved modules called RNA binding domains or RBDs. Yeah, we're talking about well-documented structures like RNA recognition motifs, case domains, helicase domains, things that are explicitly folded just to grip neucleic acids.
2:42So if we think of the cell as this massive manufacturing plant for a second, These classical RVPs are the specialized factory workers. I like that analogy. Thanks. So those RNA binding domains are their bespoke tools, like a wrench or a soldering iron designed exclusively for handling the factory's primary product, which is the RNA.
3:01Precisely. And a worker carrying a wrench isn't going to suddenly start, you know, balancing the factory's accounting books, they stick strictly to their biological mandate. That is the perfect framing.
3:11But here's where it gets interesting. Massive advancements in proteomic screening have effectively tripled the number of known RNA binding proteins over the last few years. Tripled. Wait really? Yeah, tripled.
3:24We went from a specialized cohort of a 1000 to 1000s upon thousands. And this new massive group is what the field now calls non-canonical RBPs. Okay, and here is the plot twist for you listening. These non-canonical proteins aren't some mysterious, uncharacterized novelties emerging from like the genomic dark matter.
3:45Oh, not all. Right? These are some of the most well studied famous proteins in biology, but they're known for doing completely different jobs. We're talking about core metabolic enzymes like GAPDH, which drives glycolysis, alongside various membrane channels and signaling molecules.
4:01Yeah, totally familiar. And crucially, they completely lack any of those known RNA binding domains we just talked about. which created a massive conceptual problem, right? Because for half a century, the structural assumption was that binding RNA in a meaningful way required those specialized domains.
4:16Right, you needed the wrench. Exactly. So finding 1000s of metabolic enzymes and ion channels physically clinging to RNA was just baffling. It seemed completely orthogonal to their day-to-day metabolic functions.
4:28I would assume there was a high degree of skepticism from the scientific community here, because if these enzymes don't have the specialized hands to grab RNA, and their main job is processing metabolites, I mean, we have to rule out accidental collisions.
4:43Oh, for sure. The cytoplasm is an incredibly crowded environment. Yeah, it's a dense molecular mosh pit. So how do we know these enzymes are genuinely interacting with RNA rather than just, you know, bumping into it in the chaos of the cell.
4:55Well, the standard biochemical assays couldn't really answer that, which logically led researchers to a much more definitive technology. The gold standard that proved these interactions are real and pervasive, is in Vivo UV cross-linking.
5:09Okay, shining ultraviolet light directly onto living cell cultures. I know UV light is highly reactive, but how does it separate a real functional interaction from a random microsecond collision in that mosh pit?
5:20So the photochemistry of UV cross-linking is actually remarkably precise. UB light creates covalent bonds only at what we term 0 distance. Zero distance, meaning they have to be literally touching. Exactly.
5:33It physically fuses the Urisyl basis of the RNA directly to the amino acids of the protein, but only if they are intimately structurally engaged at that exact fraction of a second. If they are merely floating near each other, the reaction just doesn't happen.
5:47Oh, wow. That's incredible Yeah, and furthermore, unlike chemical cross-linkers, you know, like formaldehyde. UV light has almost no tendency to cross-link 2 proteins together. It specifically targets and freezes that RNA protein interface without creating a massive web of false protein protein artifacts.
6:05So the UV light instantly freezes these physical connections in place. But now you just have this frozen, tangled mess of cross-linked RNA and proteins locked inside an intact cell. A total mess. You obviously have to lies or break open the cell.
6:19But how do you actually fish these specific complexes out of the cellular debris to sequence and identify them? Well, researchers develop some incredibly elegant capture methods for this. The foundational technique is RNA Interactome capture or RIC.
6:33Yeah. This utilizes microscopic magnetic beads coded with oligo DT, which are basically short strings of thymine nucleotides. These thymine strings hybridize with apollyate tales found on Messenger RNA.
6:47Ah, okay, so like a molecular magnet. Basically, when you magnetically pull the MRNA out of the cellular lysate, any protein covalently cross-linked to it just gets dragged along for the ride. Okay, that makes sense for capturing Messenger RNA, but that only represents a fraction of the transcript dome.
7:03If you want to study non-coding RNAs, You can't use a polyier bait. No you can't. So how do you separate cross-linked RNA protein hybrids from the 1000s of unlinked proteins and unlinked RNAs without relying on a specific tail.
7:16That required a leap in chemical separation, resulting in methods like OPS or fogginal organic face separation. OPS, great acronym. Isn't it? OPS doesn't rely on sequence paid at all. It uses a mixture of water, phenol, and chloroform to separate molecules by their distinct chemical properties. Oh, taking advantage of the fact that the cross-link molecule is a hybrid.
7:36So pure proteins would partition into the organic phase, while pure RNA partitions into the Aqueous phase, which means the UV cross-linked complexes must get trapped somewhere in the middle. You've hit the nail on the head.
7:48Because they are a chemical hybrid, they partition directly at the interface between the 2 liquid phases. That is so clever. It really is. They form a distinct visible disk that researchers can carefully extract, capturing all RNA species, not just MRNA.
8:03And you know, if the goal is to observe what non-canonical proteins are binding to freshly transcribed nascent RNA, researchers use a metabolic labeling technique called EU labeling. EU labeling. I assume EU stands for ethanol awarding.
8:18Got it. So you feed the cells, this modified RNA building block, the RNA polymerice incorporates into new transcripts, and then you use biorthogonal click chemistry to attach a biotin tag to that ethanol group.
8:30And that allows you to pull out only the brand new RNA. That is the exact mechanism. Yeah. Using these highly specific isolation techniques. The evidence just became irrefutable. These metabolic enzymes are absolutely physically binding to RNA inside living cells.
8:46Right. And here's where the biophysics of this gets fascinating for this deep dive, because we can chemically prove the binding occurs, but, you know, if I superglue a coffee mug to my forehead, it doesn't mean the mug is helping me write an email.
8:59Right. It just means it's stuck. So how do these non-canonical proteins physically hold the RNA without standard domains and what actually happens to the proteins function when they do? Well, to understand the binding mechanics.
9:11Structural biologists had to look beyond rigid 3D pockets. Since these proteins lack classical RNA binding domains, they utilize highly unconventional surfaces. Nearly half of the RNA binding regions identified on these non-canonical proteins are intrinsically disordered regions or IDRs.
9:29Intrinsically disordered regions, meaning they lack a fixed tertiary structure. I imagine them functioning almost like a molecular liquid rather than a rigid keyhole. A molecular liquid is a brilliant way to conceptualize it.
9:40IDRs are highly flexible, unstructured stretches of amino acids that are unusually rich in charged or aromatic residues. So they don't have a specific shape. Right, rather than providing a rigid slot for the RNA, they act as a dynamic sheath.
9:54They dynamically mold around the RNA strand, utilizing electrostatic interactions to maintain a grip. Wow. And other non-canonical RVPs take a different route. They borrow domains originally evolved for entirely different biochemical tasks.
10:07The Rossman fold, for example, is a classical ancient structural motif designed to bind metabolic cofactors like NAD plus whales. Oh, I know the Rossman folds. So they use that for RNA. Exactly. It turns out that the electrostatics of that pocket are remarkably adept at accommodating RNA as well.
10:24So they are structurally moonlighting, using dynamic electrostatic sheaths or repurposing a metabolic pocket, which leads us directly to the core discovery of the paper, the functional consequence of this finding.
10:35This is the paradigm shift known as ribo regulation. Yes. If we zoom out and look at the functional data, the realization is that RNA isn't merely being acted upon, transported, or spliced by these proteins.
10:48The RNA is actively regulating the protein's biochemical function. The instruction manual is actively dictating the behavior of the factory workers in real time. Let's ground this in the biology with some specific memorable examples of ribol regulation because the sheer variety of mechanisms here is just stunning.
11:08Let's start with protein, protein interactions and the atophagy regulator P 62. Okay, so atopage is a critical survival mechanism. It's how a cell degrades and recycles its own components to survive severe stress or starvation.
11:22For autophagy to initiate, the P62 protein must physically aggregate or oligomarize to form the scaffolding for this recycling machinery. But under nutrient rich, healthy conditions, a small non-coding RNA known as vault RNA 11 binds directly to the P 62 protein.
11:39So the RNA is functioning as a molecular bouncer. It physically parts itself on the interaction interface of P62, hysterically hindering it from oligomarizing with other P62 molecules. Exactly like about.
11:49But the moment the cell experiences starvation, the transcription of vault RNA11 drops. The bouncer leaves the door, P62 is suddenly unhindered and free to oligomarize and autophagy is immediately triggered.
12:02The elegance of that system is profound. It's a rapid signal responsive switch controlled entirely by fluctuating RNA level. That's amazing And we see an equally impressive mechanism in direct enzyme inhibition.
12:14Let's examine SHMT1, which is of vital metabolic enzyme that converts the amino acid serene into glycine, feeding the one carbon metabolic pathway. And this specific enzyme operates structurally as a tetramer, right?
12:28A symmetrical complex of 4 protein subunits working together. Correct. Structural analysis revealed that the messenger RNA of its mitochondrial counterpart, or a leading enzyme called SHMT2, binds directly to this SHMT1 tetramer in the cytosol, but the binding site's what makes this extraordinary.
12:44Where does it bind? The RNA binds to a highly flexible flap that sits adjacent to the enzyme's fully binding active site. Oh, so it's not simply plugging the active site like a competitive inhibitor. It's binding nearby, which implies an allasteric mechanism.
12:58By binding that flexible flap, the RNA must be exerting physical torque on the protein structure. Yes. That physical torque cascades through the tetramer and causes a distinct allisteric shift. It chemically distorts the geometry of the active site so significantly that serene can no longer fit into the pocket.
13:16The enzymes cleavage activity is entirely halted. So the RNA acts as a highly specific allosteric volume knob. It dials down the enzyme's activity by warping its functional shape. Exactly. And this inhibitory action scales up dramatically, doesn't it?
13:31The authors describe a glycolytic enzyme called ENO1 that experiences a phenomenon they term crowd control. Oh, I love the crowd control concept. Yeah, instead of one specific RNA transcript acting as the volume knob, ENO1 is broadly inhibited by 1000s of different RNA transcripts binding to it simultaneously, creating immense steric drag.
13:50Right, the collective mass of the cellular transcript imome, essentially slows down that specific node of the glycolytic pathway. But, you know, ribo regulation isn't exclusively inhibitory, RNA can also serve as a structural foundation.
14:02Under severe cellular stress, such as serene deprivation, long non-coding RNAs transform into physical scaffolds. The transcript glycoline NC is a prime example of this constructive riber regulation. So if the cell is starved and needs to maximize its metabolic efficiency, Glycolincy acts like a molecular party promoter.
14:24It doesn't just bind one protein. It physically tethers multiple distinct glycolytic enzymes, pulling them all together into a massive localized super complex known as a metabolon. That's a great way to put it.
14:36By physically gathering these sequential enzymes into a specialized micro compartment, the RNA facilitates substrate channeling. So the product of one enzyme is immediately handed off to the next. Exactly.
14:46Running the metabolic pathway at maximum possible efficiency to protect the cell's energy supply. Furthermore, we observe this RNA driven metabolon formation in both human cell lines and in yeast, which strongly suggests we are looking at an ancient, highly conserved evolutionary mechanism.
15:03Wow, okay. So we have RNA acting as hysteric bouncer, an allisteric volume knob and a metabolon scaffold. But there's a final example from the paper that extends this regulation into intracellular logistics, specifically, transmembrane transport into the mitochondria.
15:19Yes, this involves the ATP 5A1 protein. It's a critical nuclear encoded subunit of the ATP synthase machinery that must be imported into the mitochondria to function. And what does the RNA do there? Researchers discover that the cytosolic import of ATP 5A1 is physically facilitated by its binding to cytosolic messenger RNAs.
15:38The RNA interaction is an absolute prerequisite for its efficient translocation across the mitochondrial membrane. So the RNAX is a VIP pass structurally stabilizing or guiding the protein so it can cross the velvet rope into the mitochondria.
15:51That's exactly it. I mean, looking at P62, SHMT1, Glycolanium C, and ATP 5A1. The functional versatility of riber regulation is just undeniable. It is undeniable, but, you know, it still faces intense scrutiny.
16:05A rigorous scientific community demands that we question the biophysical reality of these interactions, especially regarding phenomena like the crowd control scene with EO1. Let me channel that skepticism for a second.
16:16A critic might look at these non-canonical RBPs and argue that these IDR mediated interactions are just low affinity, nonspecific molecular static. Right, the noise argument. Yeah. If an intrinsically disordered region is just a flexible charge string.
16:31It might weekly stick to any RNA it bumps into without any true sequence specificity. That is the dominant critique. And the researchers definitely anticipated it. First, to rule out artifacts of UV cross-linking.
16:42These interactions are rigorously validated using orthogonal assays. Like what? Well, they employ proximity legation essays or PLA, where antibodies equipped with DNA strands only generate an amplified signal, if the RNA and protein are physically touching in an uncross-linked living cell.
16:57They also use NMR spectroscopy to map the physical binding interfaces in real-time solution. So the bindings are definitely physically real. But what about the argument regarding low affinity? If the grip isn't incredibly tight, does it still count as specific regulation?
17:13This requires us to separate the concepts of affinity and specificity. Non-canonical RVPs generally exhibit lower binding affinity than a classical RNA recognition motif. They don't lock onto the RNA with the same immovable grip.
17:26Okay, that makes sense. However, a lower affinity interaction can still be exquisitely specific. Right. like a highly complex magnetic lock. The magnet itself might not be overwhelmingly strong. The affinity is low, but the geometry of the lock is so precise that it will only engage when the exact specific key is inserted.
17:45That is exactly the biophysical reality here. Even ENO1, which binds a wide array of transcripts, exhibits two orders of magnitude, greater preference for its specific target RNAs compared to non-target background RNA.
17:57Wow, 2 orders of magnitude. Yeah, that differential proves it is selective functional regulation, not just random electrostatic claim. Which brings us to the ultimate souet. If ribo regulation is this ubiquitous.
18:09The clinical implications must be staggering. We are just talking about abstract cellular metabolism anymore. We are talking about human disease. The clinical landscape is vast. When researchers cross reference these newly discovered noncanotical RVPs with the omen database, the primary catalog of human genetic diseases, the data is alarming.
18:29Really? How so? The mutation rates in these noncanonical RBP domains are extraordinarily high, mirroring the mutation rates seen in critical transcription factors. This strongly implies there is a massive, unexplored territory of genetic diseases that are currently misunderstood.
18:44Oh I see. We might be attributing a pathology to a broken metabolic enzyme when in reality, the disease is caused by a broken RNA protein reboregulatory interface. Exactly. And the virology implications are equally profound.
18:57We now have structural evidence that when RNA viruses like SARS Kofi 2 or Chikaguna infect a human cell, they actively hijack the host's metabolic enzymes. Yes. The virus repurposes our core metabolic machinery to serve as viral RNA binding proteins, utilizing our own biology to stabilize and replicate the viral genome.
19:18Which presents a completely novel therapeutic vulnerability, right? Because if pharmacologists can design small molecules that specifically disrupt the virus' ability to ribal regulate our host enzymes, we could halt viral replication without damaging the host cell's baseline metabolism.
19:34Precisely. And speaking of RNA-based therapeutics, we have to discuss the role of rival regulation in MRNA technology. Oh, this connects directly to the MRNA vaccines. The fundamental hurdle of that technology was getting synthetic RNA past our innate cellular immune defenses.
19:48Right, and those defenses are heavily mediated by non-canonical RVPs. Take 2IM 25, an E3 ubiquitant legus that functions as a primary antiviral sentinel. Okay. TIN 25's physiological role is to recognize foreign, unmodified RNA, and trigger an intracellular cascade that degrades the transcript.
20:06However, researchers discover that 2 AM 25's RNA binding is highly sensitive to specific biochemical modifications on the RNA strand. So it's looking for specific markers. Exactly. If a transcript incorporates a modification called N1 methyl pseudorodine, TRM 25's binding affinity drops to near zero.
20:23It leaves the RNA completely alone. An M1 Methylpseudodine is the exact synthetic modification bioengineers utilized in the COVID 19 MRNA vaccines. Got it. So the entire success of the vaccine platform hinges on manipulating that specific riber regulatory interface, ensuring TRM 25 ignores the therapeutic payload.
20:44Exactly. The future of MRNA medicines will rely completely on mapping and manipulating the ribo regulatory dance between therapeutic transcripts and host defense enzymes. That is just wild. But, you know, taking a step back from the modern clinical applications.
20:58I keep returning to the evolutionary timeline. We are seeing metabolic enzymes regulated by RNA and everything from simple yeast to human cell lines. It forces you to ask why. really does. Like, why would an enzyme evolve to cleave serene or process glucose simultaneously evolve to be structurally warped by an RNA transcript?
21:15Well, it leads us directly to one of the most compelling concepts in evolutionary biology, the RNA world hypothesis. This posits that billions of years ago, before the evolution of complex proteins or double standard DNA, RNA was the sole macromolecule of life.
21:31Right, because it catalyzed reactions and stored information simultaneously. Precisely. So you're suggesting that riboregulation isn't a new adaptation at all. It's a molecular fossil. When proteins finally evolved and took over the heavy lifting of cellular metabolism, the primordial RNA didn't just seed control.
21:49The evidence suggests they coevolved. As proteins became the dominant metabolic workers, RNA maintained its primordial regulatory grip. It utilized flexible IDRs and repurpose cofactor pockets to tune and adjust enzyme activity, ensuring the metabolic output perfectly matched the transcriptional state of the cell.
22:07It entirely rewrites the central dogma we started this deep dive with. We aren't looking at a rigid top-down hierarchy where proteins dominate passive RNA transcripts. We are looking at a deeply intertwined pondu, a sophisticated mutual dance, where RNA and proteins are constantly communicating, leading, and responding to each other in real time.
22:28I couldn't have said it better. If we synthesize this entirely, the central insight is this. The functional RNA binding protium is vastly larger and more structurally diverse than we ever anticipated, encompassing critical metabolic and structural proteins.
22:43RNA is not merely a passive messenger. Exactly. It is a powerful, active regulatory entity, a ribo regulator that continuously shapes protein conformation, metabolic flux and cellular survival. It fundamentally changes how you view the molecular machinery of life.
22:58what does this mean for our understanding of the origins of life? If RNA was the original master regulator and primordial cells, we have to wonder how many of our modern, intractable, metabolic diseases are actually caused by a subtle breakdown in this ancient, highly conserved RNA protein dance.
23:15It's something to think about the next time you look at a textbook diagram of a cell. This episode was based on an open access article under the CCBY 4.0 license. You can find a direct link to the paper and the license in our episode description.
23:29If you enjoyed this, follow or subscribe in your podcast app and leave a 5 star rating. If you'd like to support our work, use the donation link in the description. Now stay with us for an original track created, especially for this episode, and inspired by the article you've just heard about.
23:42Thanks for listening, and join us next time as we explore more science base by base. I thought our led to scary the light, a quiet little script in the cell at night. Then I reached for the folds and protein skin And rewired the gears from the outside in.
24:21Not just to go. Not just a trace. It finds the soft spots, it finds the space. Lower affinity sparks across the line. Turning maybe into now, in real time, RNA, on the switch. you come alive Make the enzymes lean, make the complexes drive.
24:44From I am to sugar. From stress to repair. It ties up the pieces hanging in in the air. On the switch, which, which, which, which, which, which, which, which, which, which, which, which Feel the system, oh, oh, oh, One small binding.
25:06And the wholesale group. Screams full of hits, but still gotta proof, crossing map validate, follow the groove, some contact, hiding, disordered rain, some go back to foes that don't look the same. Give me builders got for where the pathways meet, stacking up steps to a floor on the floor, heartbeat.
25:44A shadow of function, a hint of design, or a nazes, assemble in the parts, a line, are in, on the swift, watch it come alive. The enzymes lean, make complexity, drive as much as messages passing through.
26:02It's controlling binding in what to do on the switch lens re's got a DJ You didn't know the thing.
