A crowded world inside cells
Enzymes are molecular machines that drive the biochemical reactions of life. PFKP controls a key step in glycolysis, the pathway through which cells convert glucose into energy and molecular building blocks. Enzymes do not function in isolation: inside cells, they are surrounded by proteins, sugars, and many other molecules. “This molecular environment changes when cells experience stress, reorganize their metabolism, or form temporary enzyme assemblies”, explains Simon Ebbinghaus. “A key question has therefore remained open: is it mainly the limited space around an enzyme that matters, or is the chemical nature of its neighbors equally important?”
More than a matter of size, chemical surroundings tune enzyme function
To investigate this, the researchers studied PFKP in controlled solutions containing crowding molecules of different sizes and chemical properties. They measured how enzyme activity changed with temperature, assessed its structural stability, and used molecular simulations to examine interactions that cannot be observed directly in experiments.
All crowded environments reduced PFKP activity at lower temperatures. “At higher temperatures, however, the results revealed a striking difference”, says Harshita Rastogi: “Sugar-based molecules, including glucose and dextran (a glucose polymer) helped PFKP retain activity over a broader temperature range.” Because glucose and the much larger dextran had similar effects, molecular size alone could not explain the result. Instead, the findings point to the importance of “soft” chemical interactions: weak, reversible contacts among the surrounding molecules, the enzyme, and its substrates. The simulations showed that these molecules can influence regions near the enzyme’s active site, affecting both enzyme flexibility and substrate positioning.
A clue to metabolism under stress
An enzyme must be flexible enough to catalyze its reaction while holding its substrates in the correct position. Sugar-based environments appear to tune this balance, making PFKP more robust at elevated temperatures. The enzyme is not simply protected from unfolding; its dynamics and catalytic behavior are shaped by its local environment.
The study suggests that cellular crowding is not merely a physical traffic jam: “The chemical composition of the surrounding molecules may actively influence how metabolic enzymes respond to stress”, says Simon Ebbinghaus. Future research will need to determine whether cells exploit such local chemical environments to preserve metabolic activity under challenging conditions.
Angewandte Chemie International Edition
Experimental study
Cells
Soft Interactions, Rather Than Crowder Size, Determine Deviations From Arrhenius-Like Kinetics of Phosphofructokinase-1
8-Oct-2026