Thymosin alpha-1 research sits alongside two other well-characterised immune peptides that laboratories commonly work with: LL-37, the only human cathelicidin, and KPV, the C-terminal tripeptide of α-MSH. This guide covers the verified structure, origin and reported mechanism of each, how they map onto innate and adaptive immunity, and what handling and quality control the three demand. Written for researchers, in a research context only.
Key takeaways
- Thymosin alpha-1 (Tα1, thymalfasin) is a 28-residue, N-terminally acetylated peptide — Ac-SDAAVDTSSEITTKDLKEKKEVEEEAEN — cleaved from the 113-residue precursor prothymosin α, encoded by the PTMA gene. Formula C129H215N33O55, MW ≈3108 Da.
- Tα1 is described as an agonist at Toll-like receptor 2 and Toll-like receptor 9 on myeloid and dendritic antigen-presenting cells, linking innate recognition to adaptive responses.
- LL-37 is the only cathelicidin found in humans. Its 37-residue sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES (MW ≈4493.3 Da), released by proteinase-3 cleavage from the hCAP-18 precursor encoded by the CAMP gene.
- LL-37 folds into an amphipathic α-helix — a helix with segregated hydrophobic and cationic faces — which is the structural basis of its reported membrane-disrupting activity against microbial lipid bilayers.
- LL-37 also has receptor-mediated roles reported in the literature, acting as an agonist at FPRL-1, at the purinergic receptor P2X7 and at EGFR, with described effects on migration, angiogenesis and apoptosis.
- KPV is Lys-Pro-Val (C16H30N4O4, MW ≈342.4 Da), the C-terminal tripeptide of α-MSH and the shortest fragment retaining reported anti-inflammatory activity in published models.
- All three are supplied by GenoPept as lyophilised research chemicals for laboratory use only — not medicines, and not for human or veterinary use.
What are immune and antimicrobial peptides?
Immunomodulatory and antimicrobial peptides are short endogenous sequences that either act directly on microbial membranes or engage host receptors to shift immune signalling. They are typically generated by proteolytic processing of a larger precursor, which means the “active” peptide and the protein it came from are both real biological entities with distinct properties.
The three compounds in this guide illustrate the range of the category. Tα1 is a purely immunomodulatory peptide with no direct antimicrobial role. LL-37 is a classic host-defence peptide that both punctures microbial membranes and signals through host receptors. KPV is a tripeptide fragment studied almost entirely for its reported anti-inflammatory behaviour.
Nothing in this guide describes treatment of infection or disease in people or animals. It summarises what published research reports about these molecules, for use in a laboratory.
Three peptides, three biological origins
Each of these peptides is a processed fragment, and knowing the parent protein explains a great deal about the fragment’s behaviour. Tα1 comes from a nuclear protein, LL-37 from a neutrophil granule protein, and KPV from a pituitary prohormone.
Thymosin alpha-1 research: structure and reported mechanism
Thymosin alpha-1, abbreviated Tα1 and also called thymalfasin, is a 28-residue acidic peptide with the sequence Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Glu-Glu-Glu-Ala-Glu-Asn, written in single-letter code as Ac-SDAAVDTSSEITTKDLKEKKEVEEEAEN. Its molecular formula is C129H215N33O55 and its molecular weight is approximately 3108 Da.
Two structural features stand out. The peptide is N-terminally acetylated, which removes the free amino group and its positive charge. And it is strikingly acidic: the C-terminal region contains a run of glutamate residues, giving the molecule a strong net negative charge at neutral pH — the opposite of the cationic character typical of antimicrobial peptides.
Tα1 is generated by cleavage from prothymosin α, a 113-residue nuclear protein encoded by the PTMA gene. It is described in the literature as an agonist for Toll-like receptor 2 and Toll-like receptor 9 on myeloid and dendritic antigen-presenting cells, thereby stimulating adaptive immune responses. Historically, it was characterised through work on restoring immune function in animals lacking a thymus.
LL-37: the only human cathelicidin
LL-37 is the sole cathelicidin peptide found in humans, out of roughly thirty family members identified across mammals. Its name comes from its length and its first two residues: 37 amino acids beginning Leu-Leu. The full sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, giving a molecular weight of approximately 4493.3 Da.
It is stored in the secretory granules of neutrophils and macrophages as the inactive precursor hCAP-18, an 18 kDa protein consisting of a conserved cathelin domain plus the variable peptide domain. Extracellular cleavage by proteinase 3 liberates mature LL-37 after leukocyte activation. Cathelicidin production is upregulated by the hormonally active form of vitamin D, a link established by Liu and colleagues in Science (2006) and one of the more heavily cited findings in innate-immunity research.
The amphipathic helix
LL-37 adopts an amphipathic α-helical conformation. In a helix, residues four positions apart sit on the same face; by arranging cationic residues (the sequence is rich in lysine and arginine) along one face and hydrophobic residues along the other, the folded peptide becomes a molecule with a charged side and a greasy side.
That geometry is the mechanism. The cationic face is attracted electrostatically to the anionic lipid headgroups characteristic of bacterial membranes, while the hydrophobic face inserts into the acyl-chain interior — the reported basis for membrane disintegration described across the antimicrobial-peptide literature. Mammalian membranes, with a largely neutral outer leaflet and abundant cholesterol, present a different electrostatic target.
LL-37 is not only a membrane-active peptide. Published work describes receptor-mediated activity as an agonist at formyl peptide receptor-like 1 (FPRL-1), at the purinergic receptor P2X7 and at the epidermal growth factor receptor, with reported effects on cell proliferation and migration, angiogenesis and apoptosis. Reinholz and colleagues reviewed its role in inflammatory skin conditions in Annals of Dermatology (2012), and elevated cathelicidin has been implicated in rosacea and psoriasis pathogenesis in that literature.
KPV: the α-MSH C-terminal tripeptide
KPV is the tripeptide Lys-Pro-Val, corresponding to residues 11 to 13 of α-melanocyte-stimulating hormone. Its molecular formula is C16H30N4O4 and its molecular weight approximately 342.4 Da, making it one of the smallest peptides routinely handled in a research laboratory.
Its interest lies in the dissociation it represents. α-MSH carries both pigment-related activity, mediated by the His-Phe-Arg-Trp core acting at melanocortin receptors, and anti-inflammatory activity. KPV lacks the HFRW core entirely, so it cannot act as a conventional melanocortin agonist — yet published work reports that this three-residue fragment retains anti-inflammatory behaviour in model systems.
That makes KPV useful as a mechanistic tool: it separates the melanocortin-receptor arm of α-MSH pharmacology from the reported anti-inflammatory arm. It is also a component of the KLOW multi-peptide research blend alongside BPC-157, TB-500 and GHK-Cu, described in our peptide blends guide.
Practically, a tripeptide behaves very differently from a 37-mer. It is highly water-soluble, has no secondary structure to lose, and is far less prone to aggregation — but it is also small enough that trace impurities and counter-ion mass make up a proportionally larger share of vial contents.
Innate versus adaptive: where each peptide acts
The innate and adaptive arms of immunity differ in speed and specificity: innate responses are immediate and pattern-based, adaptive responses are slower, clonal and antigen-specific. These three peptides occupy different positions on that axis, which is the clearest way to hold them apart.
| Peptide | Primary arm | Studied node | Reported mechanism |
|---|---|---|---|
| Thymosin alpha-1 | Bridging innate to adaptive | Myeloid and dendritic antigen-presenting cells | Agonist at Toll-like receptor 2 and Toll-like receptor 9 |
| LL-37 (direct action) | Innate | Microbial membranes | Amphipathic helix disrupts anionic lipid bilayers |
| LL-37 (receptor action) | Innate and tissue repair | Host cells expressing FPRL-1, P2X7, EGFR | Receptor agonism; migration, angiogenesis, apoptosis effects |
| KPV | Inflammatory signalling | Epithelial and immune cells in model systems | Anti-inflammatory activity retained without the melanocortin core |
Charge tells you a lot
LL-37 is strongly cationic — the basis of its membrane targeting. Tα1 is strongly anionic, dominated by a glutamate-rich C-terminal run. KPV is small and net positive. Charge predicts solubility, adsorption behaviour and chromatographic retention, so it is the first property to check.
Size drives handling
A 37-residue helix can aggregate, adsorb and misfold; a tripeptide can do none of those things. The same generic reconstitution advice does not serve both, which is why the handling section below separates them.
Specification and comparison table
Verified identity data for the three compounds. Where a value could not be confirmed against a primary reference source it has been omitted rather than estimated.
| Property | Thymosin alpha-1 | LL-37 | KPV |
|---|---|---|---|
| Length | 28 residues | 37 residues | 3 residues |
| Sequence | Ac-SDAAVDTSSEITTKDLKEKKEVEEEAEN | LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES | Lys-Pro-Val |
| Molecular formula | C129H215N33O55 | Calculated from sequence | C16H30N4O4 |
| Molecular weight | ≈3108 Da | ≈4493.3 Da | ≈342.4 Da |
| Precursor | Prothymosin α (113 aa, PTMA) | hCAP-18 (18 kDa, CAMP) | α-MSH (13 aa, from POMC) |
| Processing step | Proteolytic cleavage | Proteinase-3 cleavage | C-terminal fragment (residues 11–13) |
| Terminal modification | N-terminally acetylated | None | None |
| Net charge at pH 7 | Strongly negative | Strongly positive | Positive |
| Other names | Tα1, thymalfasin | Cathelicidin antimicrobial peptide, hCAP-18 fragment | α-MSH(11-13), Lys-Pro-Val |
| Secondary structure | Largely unstructured in solution | Amphipathic α-helix | None |
Solution preparation: concentration reference
The table below is a concentration reference for laboratory solution preparation, converting vial mass and diluent volume into a working concentration for assay calculations. It is not a dosing table and has no application outside a laboratory.
| Mass in vial | Diluent volume | Concentration | Amount in 0.1 mL | Molarity note |
|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 500 mcg | ≈1.11 mM at LL-37 MW 4493 |
| 5 mg | 2 mL | 2.5 mg/mL | 250 mcg | ≈0.56 mM at LL-37 MW 4493 |
| 5 mg | 5 mL | 1 mg/mL | 100 mcg | ≈0.22 mM at LL-37 MW 4493 |
| 10 mg | 1 mL | 10 mg/mL | 1,000 mcg | ≈3.22 mM at Tα1 MW 3108 |
| 10 mg | 2 mL | 5 mg/mL | 500 mcg | ≈1.61 mM at Tα1 MW 3108 |
| 10 mg | 5 mL | 2 mg/mL | 200 mcg | ≈5.84 mM at KPV MW 342.4 |
| 10 mg | 10 mL | 1 mg/mL | 100 mcg | ≈2.92 mM at KPV MW 342.4 |
Molarity depends entirely on which compound is in the vial: 1 mg/mL of KPV is roughly thirteen times more concentrated in molar terms than 1 mg/mL of LL-37, because the tripeptide is thirteen times lighter. Working in molar rather than mass units avoids that trap when comparing across compounds. Full technique is in our guide to how to reconstitute research peptides.
Stability and laboratory handling
These three peptides need different handling because their chemistry differs so widely. General principles are covered in how to store research peptides; the compound-specific points follow.
- LL-37 adsorbs. A strongly cationic 37-mer binds readily to glass and to standard plastics, which at low working concentrations can remove a substantial fraction of the peptide from solution. Low-bind tubes and pipette tips are the usual mitigation.
- LL-37 can aggregate. Helical, amphipathic peptides self-associate at high concentration. Preparing the stock at a defined concentration, then diluting shortly before use, is more reproducible than holding a concentrated solution.
- Tα1 is acid-sensitive in a specific way. Its glutamate- and aspartate-rich sequence means solution pH strongly affects net charge and solubility. A well-buffered near-neutral diluent gives more consistent behaviour than unbuffered water.
- Asp-containing sequences hydrolyse. Aspartic-acid residues are the classic site of slow backbone hydrolysis and of isomerisation to isoaspartate — relevant to Tα1’s several aspartates, particularly in warm or acidic solution.
- KPV is the simplest case. Highly soluble, no structure to lose, no aggregation. Its main handling risk is arithmetic: at 342 Da the counter-ion is a meaningful fraction of vial mass.
- Aliquot everything once. Divide into single-use portions at first reconstitution rather than repeatedly freezing and thawing a single stock.
Quality control for charged and long peptides
A certificate of analysis for this group has to work harder than one for a short neutral sequence. Three specific issues arise.
First, length affects achievable purity. Solid-phase synthesis accumulates deletion sequences with every coupling step, so a 37-residue peptide will typically carry a broader impurity profile than a tripeptide made in three steps. A purity figure should always be read alongside the chromatogram.
Second, counter-ion mass matters more for small peptides. Trifluoroacetate or acetate counter-ions pair with each basic residue. For KPV at 342 Da the salt can be a large proportion of the vial contents, so net peptide content is the number that governs any concentration calculation.
Third, charge affects the chromatography itself. Highly cationic peptides such as LL-37 can tail or bind on a reversed-phase column unless the method is properly developed, which can distort an integrated purity figure. A well-documented method is part of a meaningful certificate.
GenoPept publishes per-batch third-party certificates covering HPLC purity and mass-spectrometric identity at /coa-certificates/. Our guides on reading a certificate of analysis and peptide purity testing cover the detail.
Immune research peptides in the GenoPept store
Frequently asked questions
What is thymosin alpha-1?
Thymosin alpha-1 (Tα1, thymalfasin) is a 28-residue, N-terminally acetylated peptide with the sequence Ac-SDAAVDTSSEITTKDLKEKKEVEEEAEN, molecular formula C129H215N33O55 and molecular weight of about 3108 Da. It is produced by cleavage from prothymosin alpha, a 113-residue nuclear protein encoded by the PTMA gene, and is described as a Toll-like receptor 2 and 9 agonist on antigen-presenting cells.
What is LL-37 and where does its name come from?
LL-37 is the only cathelicidin antimicrobial peptide found in humans. The name reflects its structure: it is 37 residues long and begins with two leucines. Its sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, with a molecular weight of approximately 4493.3 Da. It is released by proteinase-3 cleavage from the precursor hCAP-18, encoded by the CAMP gene.
Why is LL-37 called an amphipathic peptide?
Because when it folds into an α-helix, its cationic residues (lysine and arginine) cluster on one face and its hydrophobic residues on the opposite face. The result is a molecule with a charged side and a greasy side. That segregation is the reported basis of its membrane activity: the charged face is attracted to anionic microbial lipid headgroups while the hydrophobic face inserts into the bilayer interior.
What is KPV and how does it relate to α-MSH?
KPV is the tripeptide Lys-Pro-Val, corresponding to residues 11 to 13 of α-melanocyte-stimulating hormone. Its molecular weight is about 342.4 Da. It does not contain the His-Phe-Arg-Trp motif that melanocortin receptors recognise, so it cannot act as a conventional melanocortin agonist, yet published work reports that this fragment retains anti-inflammatory activity in model systems.
Is thymosin alpha-1 related to thymosin beta-4 or TB-500?
Only by historical naming. Both were isolated from thymic extracts, which is why they share the thymosin label, but they are unrelated in sequence, structure and reported function. Thymosin alpha-1 is a 28-residue immunomodulatory peptide from prothymosin alpha; thymosin beta-4 is a 43-residue actin-sequestering peptide, and TB-500 refers to a fragment of it.
Why does LL-37 stick to tubes and pipette tips?
LL-37 carries a strong net positive charge from its many lysine and arginine residues, and glass and standard plastic surfaces present negatively charged or hydrophobic sites that the peptide binds to. At low working concentrations this adsorption can remove a substantial proportion of the peptide from solution. Low-bind consumables, and carrier protein where the assay permits, are the standard mitigations.
Why is net peptide content especially important for KPV?
Because KPV is very small. At about 342 Da, a trifluoroacetate or acetate counter-ion pairing with its basic residue contributes a proportionally large share of the vial’s total mass. Calculating concentration from gross vial mass therefore overstates the amount of peptide present by a bigger margin than it would for a 3,000 or 4,000 dalton peptide.
What should an LL-37 certificate of analysis show?
Mass-spectrometric identity consistent with a 37-residue peptide of about 4493 Da, purity by RP-HPLC with the chromatogram and integration table included rather than a headline figure alone, the counter-ion, net peptide content, appearance and a batch number matching the vial. Because long peptides accumulate deletion sequences during synthesis, the impurity profile is as informative as the purity number.
References
- Dürr UHN, Sudheendra US, Ramamoorthy A. LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochimica et Biophysica Acta — Biomembranes. 2006;1758(9):1408-1425.
- Zanetti M. Cathelicidins, multifunctional peptides of the innate immunity. Journal of Leukocyte Biology. 2004;75(1):39-48.
- Liu PT, Stenger S, Li H, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006;311(5768):1770-1773.
- Kościuczuk EM, Lisowski P, Jarczak J, et al. Cathelicidins: family of antimicrobial peptides. A review. Molecular Biology Reports. 2012;39(12):10957-10970.
- Reinholz M, Ruzicka T, Schauber J. Cathelicidin LL-37: an antimicrobial peptide with a role in inflammatory skin disease. Annals of Dermatology. 2012;24(2):126-135.
- Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921-930. PubMed
- Reference entry: Thymalfasin — sequence, molecular formula, prothymosin α origin and Toll-like receptor 2 / 9 agonism. Reference entry
- Reference entry: Cathelicidin — CAMP gene, hCAP-18 processing, LL-37 sequence and reported receptor activity. Reference entry
Research-grade immune peptides, batch-verified
GenoPept supplies thymosin alpha-1, LL-37 and KPV as lyophilised vials with a per-batch third-party certificate of analysis covering HPLC purity and mass-spectrometric identity, dispatched from the UK, strictly for laboratory research.