Follistatin 344 Peptide

Follistatin 344 (FST344) is a single-chain glycoprotein composed of 344 amino acids that functions as a potent activin-binding protein. It was first identified in ovarian follicular fluid and subsequently found to be expressed in nearly all tissues throughout the body. Follistatin belongs to a family of activin-binding proteins that regulate TGF-beta superfamily signaling. The 344-amino acid isoform (FST344) is the precursor form that can be processed to the shorter FST315 and FST288 isoforms. FST344 is the most commonly studied form due to its broad tissue distribution and extracellular activity. For laboratory research use only.

Activin and Myostatin Neutralization Follistatin binds to activin A and activin B with high affinity (Kd ~50-500 pM), effectively preventing them from interacting with activin type II receptors (ActRIIA and ActRIIB). This neutralization blocks downstream Smad2/3 phosphorylation and transcriptional activation. Critically, Follistatin also binds myostatin (GDF-8) — a key negative regulator of skeletal muscle growth — with substantial affinity. Irreversible Ligand Trapping Unlike other TGF-beta antagonists that form reversible complexes, Follistatin forms a nearly irreversible complex with activin. The Follistatin-activin complex is then targeted for endocytic degradation, effectively removing the ligand from the extracellular environment permanently. This mechanism of action distinguishes Follistatin from soluble decoy receptors. Smad Signaling Inhibition By neutralizing activin and myostatin before they can bind to ActRII receptors, Follistatin prevents the canonical Smad2/3 signaling cascade. This pathway normally activates genes involved in growth inhibition and cellular differentiation. Blocking this pathway shifts the balance toward growth-promoting signals.