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A recent article in the scientific journal Cell regarding the function of post-translational modifications (PTM) to tubulin has demonstrated an effect of the number of PTMs on the recruitment of an enzyme that severs tubulin and tubulin degradation.

PTMs are important in controlling protein function. Examples of PTMs are ubiquitination, phosphorylation, and glutamylation of proteins.

Tubulin is a globular protein that polymerizes to form long chains or tubulin fibers, called microtubules. Alpha- and beta-tubulin proteins form dimers that attach to a growing spiral tube of these protein dimers.

Degradation of tubulin is controlled by its glutamylation. Glutamates are added to tubulin by glutamylase. The enzyme spastin binds to the glutamates and severes tubulin.

The graph below shows the effects of the number of glutamates attached to tubulin on tubulin degradation.

From the data shown in the graph, what is the effect of the number of glutamates on tubulin degradation?

The requested supplement was not found.
A

Without glutamylation tubulin is degraded at a steady moderate rate, but with the addition of glutamates (around 4 glutamates), the degradation drops off rapidly.

B

Without glutamylation, tubulin is not degraded; upon glutamylation, spastin is recruited and begins degrading tubulin with further glutamylation resulting in continuous degradation until the tubulins are completely degraded and do not polymerize again.

C

Without glutamylation, tubulin is not degraded; upon glutamylation, spastin is recruited and begins degrading tubulin with further glutamylation (8 and above glutamates) resulting in an elimination of tubulin degradation.

D

There is no effect of glutamylation on the degradation of tubulin.

E

Glutamylation is not required but the addition of multiple spastins is critical to tubulin degradation.

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