Myostatin Propeptide

1 Identity

Recombinant protein - neither a small molecule nor a chemically synthesizable peptide. The N-terminal prodomain of human myostatin (GDF-8, gene MSTN, UniProt O14793), approximately residues 24-266 once the signal sequence is excised, about 240 to 244 residues, expressed in E. Coli or a mammalian line and refolded, with an unfused monomer sizing near 28 kDa. At greater than 40 amino acids with a specific defined sequence it is a protein rather than a peptide. Not a synonym for mature GDF-8/myostatin, which is the other half of the same precursor, is sold under the bare word 'Myostatin', and is a different article. Not a synonym for the GDF-11 (BMP-11) prodomain.

Sequence

The sequence depends on the construct, so it has to be taken from the manufacturer's own datasheet rather than assumed from the parent protein. Residue numbering must be fixed against UniProt O14793 and against the supplier's own construct map, not against this record. Traded material differs between suppliers in the truncation boundary at both ends, in whether an Fc fusion partner is present, in affinity-tag chemistry and position, in expression host and therefore in glycosylation. Cysteine count and disulfide connectivity are construct-dependent and cannot honestly be asserted in the abstract. At this length the article is not accessible by solid-phase synthesis, so there is no synthetic route that would fix the sequence independently of the construct.

Molecular formula

Not established, and not establishable in the abstract. No single construct defines the article, and a molecular formula for a glycosylated, possibly tagged, possibly Fc-fused recombinant protein is a property of the construct and the expression host rather than of the product name.

Average mass

Not established. No formula exists to compute from, so no average mass is printed here. The '28 kDa' figure is a sizing estimate consistent with a 240-residue polypeptide, not a computed mass, and it must never migrate into a certificate acceptance window. The single most instructive observation in the commercial record makes the point: one supplier's own datasheet, for a single His-tagged mouse propeptide construct expressed in a mammalian line, states a PREDICTED mass of 28.7 kDa and an observed 39 kDa on reducing SDS-page for the same item, a 10.3 kDa gap attributable to glycosylation and the 10-His tag.

Monoisotopic mass

Not established and not meaningful for this class. A monoisotopic mass is not a usable acceptance attribute for a roughly 28 kDa glycoprotein: the isotope envelope of a molecule of this size is not resolved as a monoisotopic peak on routine instrumentation, and glycan heterogeneity makes intact mass a distribution rather than a value. A mass on this class of certificate is not an identity. Identity for this class is established by peptide mapping with LC-MS/MS sequence coverage and disulfide assignment against a qualified reference standard, not by an intact number.

Salt / variant note

Five materially different molecules trade in this space and at least four are sold under a name containing 'myostatin propeptide'. (1) One supplier's construct: human, E. Coli, 244 amino acids, non-glycosylated, untagged, stated 27.8 kDa, >95 percent by SDS-page. (2) A second supplier's construct: mouse GDF-8 propeptide, Asn25-Ser265, NS0 mouse myeloma, C-terminal 10-His tag, predicted 28.7 kDa, observed 39 kDa reduced, >90 percent by silver-stained SDS-page. (3) A third construct from that same supplier: mouse GDF-8 propeptide Fc chimera, Asn25-Arg267 carrying a Ser265Arg substitution, fused to mouse IgG2A Glu98-Lys330, predicted 54.9 kDa per monomer, observed 66 kDa reduced, roughly 110 to 130 kDa as the inter-chain disulfide-linked homodimer. (4) Mature GDF-8/myostatin itself, catalogued in both a research grade and a GMP grade: the 109-residue C-terminal domain, roughly 12.4 kDa as a monomer and roughly 25 kDa as the disulfide-linked homodimer. It is the other half of the same precursor, cheaper to express, and it is sold under the bare word 'Myostatin'. (5) The GDF-11 (BMP-11) prodomain: a close homolog of similar size that co-migrates on a gel and is not separated by a nominal intact mass - only peptide mapping with LC-MS/MS coverage across the divergent regions distinguishes the two. Further construct variants are catalogued by at least six other reagent suppliers, each with its own boundary and tag. A consumer-market article sold as 'Myostatin 1 mg' copies the first construct's descriptive numbers (244 amino acids, 27.8 kDa) while simultaneously describing the protein as supplied 'with tags', which that untagged construct is not.

2 Class & testing panel

Form

Single article

Testing panel

P4 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists and is predominantly mouse and livestock genetics, plus a targeted structural literature. Foundational: McPherron AC, Lawler AM, Lee SJ, Nature 1997;387:83-90. That work is followed by transgenic and knockout studies in mice and by cattle and sheep genetics. Human interventional literature on myostatin propeptide itself was not identified. Human trials do exist elsewhere on the same pathway and belong to different molecules: the anti-myostatin monoclonal MYO-029 (Wagner KR et al., Ann Neurol 2008;63:561-571), bimagrumab, and ACE-031, each of which is a separate article with its own record. The citation index badges those unmistakably as different molecules, because conflating a propeptide with an antibody or an ActRIIB decoy receptor is the standard error in the gray-market literature on this compound. No registered studies under this identity are listed on ClinicalTrials.gov.

4 Storage & specification

Storage

Lyophilized material is held at -80 degrees C in single-use aliquots; formulated solution is held at 2 to 8 degrees C, with the buffer, the carrier protein and the freeze-thaw limit stated on the label rather than left to the user. Aliquot volumes are set to the working volume and thawed aliquots are not refrozen, because repeated freeze-thaw is the failure mode that matters for this class. Where the declared construct's own datasheet states a narrower condition, that condition governs.

Shelf life

The retest interval is construct-specific and is set for each declared construct from that construct's own aggregation data by SE-HPLC against a qualified reference standard, with the resulting retest date printed on the vial and enforced first-expiry-first-out. The attributes that limit it are aggregation and fragmentation by SE-HPLC, purity by SDS-page, and identity by peptide mapping with LC-MS/MS coverage against the same reference standard. No catalog-wide interval is applied across constructs, because the truncation boundary, the tag, the fusion partner and the expression host differ from one construct to the next.