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Activin-binding glycoprotein isoform

Follistatin-315

Follistatin-315 (FS-315) is the longer of two follistatin isoforms generated by alternative splicing of the FST gene. Follistatin binds activin and related TGF-beta ligands, including myostatin. FS-315 is an investigational research protein, not authorized by Health Canada; this page is educational only.

By The Peptides Codex Editorial TeamReviewed July 10, 2026
Length
315 aa
Class
Activin-binding glycoprotein isoform
Function
Binds and neutralizes activin and other TGF-beta family ligands
Context
Investigational research protein; not authorized by Health Canada

The circulating splice isoform of follistatin, distinct from the FS-288 form.

Also known as: FS-315 · FST-315

Part of the Growth hormone & IGF peptides cluster

Overview

Follistatin-315 (FS-315) is the longer of two follistatin isoforms generated by alternative splicing of the FST gene. Follistatin binds activin and related TGF-beta ligands, including myostatin. FS-315 is an investigational research protein, not authorized by Health Canada; this page is educational only.

Source & context

Biological / chemical source: Longer splice isoform of human follistatin (FST gene)

Primary research or clinical context: Investigational research protein; not authorized by Health Canada

Two isoforms

Alternative splicing of the FST transcript yields FS-288 and FS-315. FS-315 has an acidic C-terminal tail that lowers its affinity for cell-surface heparan sulfate, so it circulates more freely, whereas FS-288 binds tightly to cell surfaces. Both act by sequestering activin and related ligands.

Research interest and status

Because follistatin can bind myostatin, a negative regulator of muscle mass, it draws interest in muscle-biology research. Human data specific to administered follistatin proteins are limited. FS-315 is investigational, is not an approved drug in Canada, and this summary makes no therapeutic or performance claims.

FAQ about Follistatin-315

What is Follistatin-315?+

Follistatin-315 (FS-315) is the longer of two follistatin isoforms generated by alternative splicing of the FST gene. Follistatin binds activin and related TGF-beta ligands, including myostatin. FS-315 is an investigational research protein, not authorized by Health Canada; this page is educational only.

Is Follistatin-315 an approved medicine?+

Follistatin-315 is discussed here as a research / educational topic. Investigational research protein; not authorized by Health Canada. This is not medical advice.

What is the typical length of Follistatin-315?+

Follistatin-315 is commonly described as approximately 315 amino acids (Activin-binding glycoprotein isoform).

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References & further reading

  1. 1.Wikipedia — Follistatin
  2. 2.NCBI Gene — FST follistatin (Gene ID 10468)
Disclaimer: Educational content only. Not medical advice. Not instructions for human use. Research peptides and unapproved products may be restricted or illegal to market for human consumption in your jurisdiction. Consult qualified professionals and applicable law.
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Cite this: Peptides Codex — Follistatin-315 educational profile.
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