A breakthrough in understanding the inner workings of cells has been achieved by researchers at Washington University. They've developed a method to measure a key property, pH, within cellular condensates, unlocking a new level of detail about these enigmatic structures.
Condensates are like bustling marketplaces within the cell. Made up of proteins and nucleic acids, they lack a surrounding membrane but assemble and disassemble dynamically as needed. The nucleolus, a prominent condensate, plays a crucial role in building ribosomes, the protein factories of the cell. Defects in nucleolar function are linked to diseases like cancer and neurodegeneration.
Led by Dr. Rohit Pappu, the team at Washington University is the first to map the internal organization of these condensates. Their research, published in Cell, reveals that different condensates have distinct pH levels. The nucleolus itself has an acidic environment, while other condensates like nuclear speckles have a neutral pH, similar to the surrounding cellular fluid.
This discovery sheds light on how condensates assemble. The researchers identified unique "molecular codes" within nucleolar proteins, including stretches of acidic amino acids, that likely act like magnets for protons (hydrogen ions), creating the acidic environment.
Imagine condensates as social gatherings. Specific topics ("molecular grammars") draw certain individuals together, while others stay on the periphery. This interplay of interactions gives rise to emergent properties, like the unique pH within the nucleolus.
The formation of condensates, termed "condensation," combines two processes: phase separation, like oil separating from water, and sticky interactions between molecules. "The specific interactions and solubility profiles of biomolecules dictate how they assemble," explains Dr. Matthew King, lead author of the paper. "This assembly gives rise to emergent properties, like the unique pH signature in the nucleolus."
This research paves the way for understanding how the whole of a condensate becomes greater than the sum of its parts. The differences in pH create a "proton motive force," which could guide the movement of RNA and proteins crucial for ribosome assembly.
Reaching into these tiny cellular compartments required innovative tools developed by the team, including collaborations with colleagues at Washington University.
"This work," says Dr. Pappu, "addresses a major criticism of condensates – that they are just messy blobs." The research reveals that these "blobs" have a well-defined internal order, with distinct properties that may explain how they carry out specific cellular functions.
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