Follistatin-344

Follistatin-344 (FST-344) is the longer alternatively-spliced isoform of human follistatin, a secreted regulatory glycoprotein encoded by the FST gene (canonical UniProt P19883). The “344” is the length in amino acids of the primary translation product, counting the 29-residue signal peptide; once that signal peptide is removed, the mature secreted protein is 315 residues (FS-315, residues 30–344). A shorter splice isoform gives the 288-residue mature form (FS-288), and a C-terminally truncated proteolytic product is known as FS-303 — so the “344” label specifically denotes the longer precursor, not a 344-residue mature chain. Follistatin is heavily disulfide-bonded (every cysteine is paired) and, importantly, it is glycosylated: recombinant mature follistatin migrates at roughly 40–50 kDa on SDS-PAGE, above its ~34.7 kDa polypeptide mass, because of attached N-linked glycans. That glycosylation makes the protein’s mass heterogeneous, so no single exact molecular formula or monoisotopic mass describes it — its identity is captured instead by its sequence, its UniProt and PDB cross-references, and a stated mass range. At the molecular level, follistatin is characterized as a high-affinity binding partner for activin and related TGF-β-superfamily ligands; the deposited crystal structure of the follistatin–activin complex shows two follistatin molecules encircling the activin dimer. Lineará lists Follistatin-344 as a characterization-only reference entity. For Research Use Only — Not for Human or Veterinary Use.