Follistatin 344 Peptide (FS-344)

The rough draft of a protein, sold under the finished draft's reputation.

Follistatin 344 refers to the 344-residue unprocessed human follistatin precursor, UniProt P19883, which includes a 29-residue signal peptide at positions 1 to 29 and a mature chain at positions 30 to 344. The circulating protein is the 315-residue mature form, a glycoprotein containing 36 cysteines that binds and neutralises activins as well as myostatin.

Protein names hide a lot of biography, and this one hides the important part.

Follistatin-344 is the precursor: the full first-pass translation, signal peptide still attached, before the cell processes it into the working protein.

Thirty-six cysteines is an enormous folding problem. The protein's function lives in that folded architecture, not in the bare sequence.

So the question a careful buyer asks is not what is follistatin, it is which follistatin, in what fold.

A precursor with the famous name, where the fame belongs to the finished product.

The famous myostatin-binding belongs to the folded, processed form.

Follistatin's claim to fame is real and beautifully simple: it binds and neutralises myostatin, the signal that tells muscle tissue to stop growing.

A brake on the brake. No wonder the internet noticed.

Which is why the gene-therapy route exists: deliver the gene, let the cell do its own manufacturing and folding, and you sidestep the problem entirely.

Here's the honest part about any vial of this.

For a 36-cysteine protein, folding verification is the entire product question, and a purity percentage does not answer it. Purity says the right atoms showed up. It says nothing about whether they folded.

Gene-therapy trials built this name. A vial is not gene therapy.

The exciting follistatin results in the literature come from a specific place, and it is not a vial.

The headline animal work and the small human trials in muscular dystrophy used gene therapy, viral vectors delivering the gene so cells produce properly folded protein in place.

Direct administration of the protein itself has a far thinner file, precisely because of the folding and delivery problems above.

Nothing approved. Prohibited in sport, category S4, named class.

A real and fascinating biology, a borrowed evidence base, and a folding question no COA can close. Those three sentences are the honest product page.

The 344 in the name is precursor numbering. It counts the 29-residue signal peptide the cell removes during secretion. FS-315 is the predominant serum isoform and FS-288 is the shorter splice variant. Check which molecule a paper or a label is actually describing before comparing them.

This is a glycoprotein, not a synthesisable peptide. Thirty-six cysteines and two N-glycosylation sequons in a 315-residue chain rules out solid-phase peptide synthesis. Recombinant expression is the only route, and glycosylation means observed mass runs above the bare polypeptide figure.

Canadian regulatory status. Health Canada states peptides are generally regulated as prescription drugs and that For Research Use Only labelling does not make a product legal or exempt from regulatory requirements. This is sold as laboratory material, not for human or veterinary use.