SNAP-25: the protein that botulinum toxin cleaves

SNAP-25 is a protein located in the terminal of the motor nerve. It is part of the group of proteins called the SNARE complex, which lets vesicles full of acetylcholine fuse with the membrane of the nerve cell and release the neurotransmitter at the neuromuscular junction. Without this fusion, the muscle does not receive the signal to contract. This is exactly the point that type A botulinum toxin attacks.

How does the toxin reach SNAP-25?

The toxin is a protein with two functional parts, a heavy chain and a light chain. The heavy chain binds to the nerve terminal and carries the molecule into the cell. The light chain, which has enzyme activity, is released inside the terminal and cleaves SNAP-25 at a specific point. With the protein cleaved, the SNARE complex does not assemble properly, the vesicle does not fuse and acetylcholine stops being released in sufficient amounts.

The result is so-called chemical denervation: the nerve is still there, but the muscle is no longer stimulated as before. Because each fiber is affected at its own pace, the effect appears gradually, over the interval described in toxin latency.

Why does the effect wear off?

The cleavage of SNAP-25 is reversible. The nerve terminal synthesizes new protein and, in the meantime, sends out small sprouts that create temporary connections with the muscle fiber. Over time, the original function is restored and contraction returns to its prior level. This relates to what the clinic calls toxin rebound effect and explains the need for repeat injections for those who want to keep the result.

What about other serotypes?

Not every serotype acts on SNAP-25. Some cleave another protein of the same complex (such as VAMP or syntaxin). For aesthetic practice, what matters is knowing that the products in common use in facial harmonization are serotype A, and that the difference between them is not only in the name. See the comparison in toxin serotypes.

Relationship to planning and safety

Understanding the mechanism helps answer frequent questions: why the result is not immediate, why it is not the same in every patient and why neighboring muscles can be affected when the toxin spreads beyond the target (see toxin diffusion). The dose, the choice of muscle and the technique are at the discretion of the qualified professional, after assessment, according to the rules of their professional board in Brazil. The concept of the motor unit completes this picture.

In Harmy

The Glabella marking in the app serves as a visual reference for talking about the area. Harmy does not simulate the toxin's effect on the musculature: the projection is an illustrative image, generated by AI, and does not predict an individual's response.

Also called: synaptosomal-associated protein of 25 kDa.