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The Penn State Protein Ladder after protein electrophoresis and staining with Coomassie Blue dye

The Penn State Protein Ladder system

An inexpensive resource for the protein-research community
18 August 2021

Labs can easily make their own protein ladders for less than a penny per experiment using the newly developed, license-free “Penn State Protein Ladder system.” A research team of undergraduate students led by Song Tan, Verne M. Willaman Professor of Molecular Biology at Penn State, developed the ladders to be easily used in two of the most common experiments—SDS-PAGE and Western blots—in protein research.

A paper describing the research appears August 18, 2021 in the journal Scientific Reports.  This paper was coauthored by Ryan T. Santilli, John E. Williamson III, Yoshitaka Shibata, Rosalie P. Sowers, and Andrew N. Fleischman, all of whom were Penn State undergraduate students.

“It has been exciting and rewarding to develop this project from just an idea to tools that can serve science,” said Williamson.

Protein ladders are molecular rulers for estimating the sizes of proteins separated by gel electrophoresis.

“Any lab working with proteins uses these ladders on a daily basis and the cost for commercially available ladders adds up—averaging about $1.00 per experiment,” said Tan. “Our Penn State Protein Ladders can be easily made for a tiny fraction of that cost using source material that we make available to nonprofit academic researchers through the Addgene and DNASU plasmid repositories.”

The Penn State Protein Ladder after protein electrophoresis and staining with Coomassie Blue dye
The Penn State Protein Ladder after protein electrophoresis and staining with Coomassie Blue dye. Individual proteins are shown together with the combined protein ladder on the right. Credit: Song Tan, Penn State

The Penn State Protein Ladder is composed of nine proteins that range in molecular weight from 10 to 100 kilodaltons (kD). Each protein is encoded on an individual plasmid—a circular form of DNA—that is expressed at very high levels in the bacteria E. coli. Using standard laboratory protocols, researchers can grow E. coli cells containing the plasmids and then purify the proteins using a common affinity tag designed into each protein. 50 milliliters (ml) of cells produce enough of each individual protein for 20,000 experiments.

“Researchers can pick and choose amongst the nine individual proteins to design a ladder optimized for their research project,” said Tan. “They might not need the entire set, or they might want to individually control the intensity of bands produced on a gel. This customization is easy to accomplish with the Penn State Protein Ladder system”

For even more efficient production, the ladders are also available as two coexpression vectors that produce either the set of 10, 30, 50, 100 kD proteins or the set of 20, 40, 60, 80 kD proteins. All the ladder proteins can be stained using dyes such as Coomassie Blue and are also directly detectable in Western blots through the incorporation of immunoglobulin antibody binding domains.

The Penn State Protein Ladder team
The Penn State Protein Ladder team: (Back from left) Yoshitaka Shibata, Jack Williamson, Song Tan. (Front from left) Ryan Santilli, Rosie Sowers. Not shown: Andrew Fleischman. Credit: Song Tan, Penn State

"We are thrilled to share these reagents with the global scientific community,” said Santilli.

Undergraduate students working with Tan previously developed the Penn State DNA ladder, which allows researchers to produce their own DNA ladders for about a penny per experiment.

“Inexpensive and easy to use laboratory reagents like these help to democratize science by making it accessible to more labs and schools around the world,” said Tan. “The Penn State DNA ladders have been requested by almost 500 labs on every continent except for Antarctica. We hope that the Penn State Protein Ladders will be similarly useful to the research community.”

This research was supported by the U.S. National Institutes of Health, the Penn State Eberly College of Science, and the Penn State Schreyer Honors College.

Media Contacts
Song Tan
Professor of Biochemistry and Molecular Biology
Sam Sholtis
Science Writer