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Coacervate droplets as pH-regionalized protocells

2026-02-02 · Back to index

Why tiny droplets matter for life’s chemistry

Inside our cells, countless chemical reactions must run at just the right speed and under just the right conditions to keep us alive. One of the most important of these conditions is acidity, often described by pH. Yet some of the busiest “workplaces” in the cell, called membrane-less organelles, have no surrounding membrane or pumps to set their pH. This study explores how simple, droplet-like structures made from short peptides can mimic these organelles, create their own tiny pH zones, and control complex reactions like copying DNA and making proteins—offering clues to both modern cell biology and how the earliest protocells on Earth might have functioned.

Hidden pH zones inside the cell’s control center

The authors begin with the nucleolus, a large droplet-like compartment inside the cell nucleus that helps build ribosomes, the protein factories of the cell. Using a fluorescent dye that changes color with pH, they measured acidity inside the nucleolus and in the surrounding nucleoplasm in several cell types. They found that the nucleolus is consistently slightly more acidic than its surroundings, revealing a built-in pH difference across this invisible boundary. When they treated cells with drugs that disturb nucleolar activity or structure, this pH contrast shrank or disappeared, linking the local acidity not to membrane pumps but to the very existence and health of the droplet-like structure itself.

Building synthetic droplets that split acidity

To study this effect under controlled conditions, the team built an artificial system

using “coacervate” droplets made from two simple ten–amino acid peptides, one positively charged and one negatively charged. Mixed in water, these chains separate into a dense droplet phase and a surrounding dilute phase, resembling a stripped-down version of a membrane-less organelle. By carefully adding small amounts of acid or base and then measuring pH inside and outside the droplets, they showed that the dense phase becomes either more acidic or more alkaline than the surrounding solution. Computer simulations supported this picture: hydrogen and hydroxide ions are drawn into the charged network of the droplet and move more slowly there, creating a stable pH difference that fades when the droplets are dissolved by salt. In other words, phase separation alone can carve out tiny chemical niches with distinct acidity.

Turning droplets into working mini-reactors

Next, the researchers loaded these peptide droplets with real enzymes that naturally change pH as they work. One enzyme, glucose oxidase, converts sugar to an acid, shifting its environment toward lower pH. Another, urease, breaks down urea to produce basic products that raise pH. The enzymes spontaneously concentrated inside the droplets because of attractive charge-based interactions with the peptide chains. When their substrates were added, the interior of the droplets shifted its pH more strongly than the surrounding solution, and this tuning range could be widened or narrowed by adjusting droplet composition and salt content. Despite the crowded interior, the enzymes remained active, though their speed and apparent affinity for substrates differed from those in plain solution, reflecting the special microenvironment inside each droplet.

Programming reaction cascades with local acidity

With controllable pH zones in hand

, the team asked whether one reaction inside a droplet could turn another reaction up or down. Because each enzyme prefers a certain pH, the acid-producing glucose oxidase could dampen urease, and the base-producing urease could suppress glucose oxidase, creating a simple chemical cross-talk. The authors then stepped up the complexity: they used the droplets to host polymerase chain reaction (PCR), which copies DNA, and a cell-free transcription–translation system, which reads DNA into RNA and then into protein. By letting the pH-shifting enzymes run before these genetic reactions, they could either support or inhibit DNA copying and protein production, simply by changing whether the droplet interior became more acidic or more basic.

What this means for cells and protocells

Taken together, the work shows that droplets formed by phase separation can naturally create and maintain small but meaningful pH differences—without membranes, pumps, or elaborate machinery. In living cells, similar condensates may use this principle to fine-tune which reactions happen where and when, helping organize metabolism and gene control in space. In the context of early life, such coacervate droplets act as plausible protocells, offering sheltered environments where key reactions like copying genetic material and making simple proteins could be guided by local chemistry alone. By demonstrating precise pH control and complex reaction chains in these minimal systems, the study points toward both a deeper understanding of modern cellular organization and new tools for synthetic biology that harness phase-separated droplets as programmable, pH-tuned microreactors.

Citation: Wang, C., Fang, Z., Zhang, L. et al. Coacervate droplets as pH-regionalized protocells. Nat Commun 17, 2252 (2026). https://doi.org/10.1038/s41467-026-68980-6

Keywords: membraneless organelles, phase separation, coacervate droplets, pH regulation, protocells