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The Proteasome

More About Proteasome

Once a protein has completed its job in a cell it is typically disposed of, to insure that it does not continue to function when no longer needed, and to recycle it’s component amino acids. The proteasome is a multiprotein structure thatcells employ to destroy and recycle unwanted proteins. Several molecules specifically tag proteins destined for destruction. Without the tags, useful proteins might be degraded as well those no longer wanted. In this animation the protein to be degraded is Ataxin-1 shown in yellow. Ubitquitin, shown in pink, is the molecule that tags Ataxin-1 proteins targeted for degradation. Ubiquitin is carried to Ataxin by a carrier enzyme shown in orange. Another enzyme, ubiquitin ligase, interacts with the carrier enzyme, helping it to attach ubiquitin to Ataxin-1. Once a single ubiquitin has been attached to Ataxin-1 other ubiquitin molecules are drawn to the site to forma long chain that the proteasome will recognize as an indicator that this particular Ataxin-1 molecule is to be degraded.

The proteasome is a bit like a garbage disposal, withfour core units and a cap on either end. With the help of ubiquitin, bound Ataxin-1 triggers the cap to open and the Ataxin-1 molecule unfolds and enters the central core of the proteasome. The proteins of the proteasome core break Ataxin-1 down into peptide fragments and amino acids. The fragments empty out the other end of the proteosome for further degradation and recycling.

The proteosome can have a problem digesting certain mutant forms of proteins. In the case of Ataxin-1, mutation can create a shape that is unable to unfold and enter the proteasome. As a result, mutant ataxin accumulates in the cell. The build-up of mutant protein may eventually kill the cell by gumming up the works and interfering with essential cellular functions. This mechanism may be responsible for the cell death and symptoms seen in the diease Spinocerebellar Ataxia Type 1, and others.

Proteasome Background

Spinocerebellar ataxia Type 1 (SCA1) is a neurological disorder that strikes later in life between the ages of 30-40. Patients with SCA1 experience a deterioration of balance and coordination that renders them unable to walk or talk clearly, or eventually to even swallow or breathe. It is thought that the disease could be related to a build up of a mutated form of ataxin-1 in neural cells.

From Lecture three of the 2003 Holiday Lectures Series "Learning From Patients: The Science of Medicine."

Proteasome Teaching Tips

The animations in this section have a wide variety of classroom applications. Use the tips below to get started but look for more specific teaching tips in the near future. Please tell us how you are using the animations in your classroom by sending e-mail to biointeractive@hhmi.org.

  1. Use the animations to make abstract scientific ideas visible and concrete.

  2. Explain important scientific principles through the animations. For example, the biological clocks animations can be used to demonstrate the fundamentals of transcription and translation.

  3. Make sure that students learn the material by repeating sections of the animations as often as you think necessary to reinforce underlying scientific principles. You can start, restart, and play back sections of the animations.

  4. Urge students to use the animations in accordance with their own learning styles. Students who are more visually oriented can watch the animations first and read the text later, while others might prefer to read the explanations first and then view the graphics.

  5. Incorporate the animations into Web-based learning modules that you create to supplement your classroom curricula.

  6. Encourage students to incorporate the animations into their own Web-based projects.

Resources

The 2003 Holiday Lectures Series "Learning From Patients: The Science of Medicine."

Proteasome Credits

Director: Dennis Liu, Ph.D.

Scientific Direction: Bert Vogelstein, M.D.

Scientific Content: Satoshi Amagai, Ph.D.

Animator: Eric Keller

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