Professor Publishes Study on Polymers Moving Into a Crowded Cell

MERCED - When material needs to cross the membrane into a living cell, speed is critical. Fuel, chemical signals and genetic information must be delivered at the right time so that cells can perform essential functions like fighting off disease or producing new cells.

The polymers, or long chains of proteins, that provide those intracellular signals aren't crossing into open space. The inside of a cell is crowded with organelles, free-floating proteins and the jungle-gym-like structure of the cell skeleton.

In a surprising finding published in the journal Physical Review Letters, Professor Ajay Gopinathan of the School of Natural Sciences at the University of California, Merced, and his colleague Young Woon Kim at the Korea Institute for Advanced Study have concluded that over an extremely large range of lengths, the time it takes for a polymer to cross the cell membrane into the crowded interior remains essentially constant.

"Understanding how cells communicate with each other and with their microenvironment and how they respond to changes in their environment is fundamental to understanding cell function in normal development and in health and disease. Ajay's innovative work on polymers lends insight into how signals from the environment can be delivered into cells and how polymers traverse the dense packing inside the cell," said Dean Maria Pallavicini of the School of Natural Sciences. "His work is an important, interdisciplinary piece of the big picture of biomedical research at UC Merced."

"It's as if you had a length of chain sitting on a table, and you wanted to feed the chain over a large bump and through a hole in the table to the floor," Gopinathan explained. "For the first little while you would have to feed it through the hole link by link, but after a certain point there would be enough force from the other side to pull the entire chain through very quickly."

In that illustration, the force is gravity, but for polymers crossing membranes, the force comes from structures within the cell binding to the polymer. Once a sufficient number of them can grasp the end of the chain, the entire structure can traverse a pore in the cell membrane very quickly. That means the time it takes for a polymer to cross is determined by how fast the initial part of the chain pushes through the pore.

Gopinathan said this mechanism may facilitate the delivery of multiple polymers of different lengths across pores at the same time - but as with all scientific questions, more work remains to be done. The researchers hope next to investigate how charges and polymer networks may affect how materials cross cell membranes.

The study was funded by the National Science Foundation and by Gopinathan's start-up funding at UC Merced.

Gopinathan joined the faculty of UC Merced in 2006 following a postdoctoral research appointment at UCSB. He is involved with undergraduate programs in physics and applied mathematics along with his research. He earned in Ph.D. in 2003 at the University of Chicago.

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