Semax Peptide: Structure, Binding, and Gene Expression

For laboratory and research use only. Not for human consumption.

A rat study reported an increase in exon III BDNF mRNA in the hippocampus, with BDNF protein and TrkB phosphorylation measured as separate endpoints (Dolotov et al., 2006). These were molecular measurements in that animal model.

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. It is an analogue of the ACTH fragment spanning residues 4 to 10. Its Pro-Gly-Pro C-terminal segment has been studied in relation to enzymatic stability and molecular signaling. The published literature includes binding assays and analyses of gene and protein expression in rodent tissue.

What Is Semax?

Seven amino acids: MEHFPGP. Semax is a synthetic analogue of the ACTH fragment spanning residues 4 to 10. Its sequence contains Met-Glu-His-Phe followed by Pro-Gly-Pro.

• Sequence: Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP)
• Classification: Synthetic analogue of ACTH residues 4 to 10, with a Pro-Gly-Pro C-terminal segment
• Molecular Weight: ~813.97 g/mol
• Length: Seven amino acid residues

The Pro-Gly-Pro segment is relevant to enzymatic stability and has also been studied as a separate peptide.

Development Story

Semax was developed in the 1980s by Nikolay Myasoedov’s laboratory at the Institute of Molecular Genetics, Russian Academy of Sciences. The same institute developed Selank. The work examined changes to ACTH-derived peptide sequences, including their enzymatic stability and molecular activity.

Much of the published research appeared in Russian-language journals. Later studies used transcriptomic and proteomic methods to examine Semax-associated changes in gene and protein expression.

The preclinical literature includes binding assays, rodent tissue analyses, and gene-expression studies. These methods examine different experimental endpoints.

Chemistry and Structure

The Met-Glu-His-Phe segment corresponds to ACTH residues 4 to 7. In Semax, it is followed by Pro-Gly-Pro rather than the Arg-Trp-Gly segment of ACTH residues 8 to 10. That substitution gives Semax a distinct sequence.

That PGP tail warrants attention.

Mechanism of Action: BDNF Is the Headline, But Not the Whole Story

Semax studies have examined BDNF/TrkB signaling alongside other molecular endpoints. The findings come from different assays and tissue models, so they should be considered separately.

BDNF and TrkB Measurements

A Brain Research paper (PMID: 16996037) examined BDNF and TrkB measurements in rat hippocampal tissue.

The reported timing describes that rat experiment. Comparing it with another study requires matching the tissue, collection time, and analytical method.

In rat basal forebrain preparations, tritium-labeled Semax showed reversible, calcium-dependent binding, with a K_D of 2.4 ± 1.0 nM and a B_MAX of 33.5 ± 7.9 fmol/mg protein. These measurements described binding sites, not the molecular identity of a receptor. Separate rat tissue measurements reported a BDNF response in the basal forebrain but not the cerebellum.

NGF and Neurotrophin-3

In rat permanent middle cerebral artery occlusion (pMCAO) experiments, Semax-associated increases were reported in the expression of NGF, NT-3, and neurotrophin receptors TrkA, TrkB, and TrkC. The timing and magnitude varied by brain region and time after occlusion (PMC11498467).

Dopamine and Serotonin

Eremin et al. examined dopaminergic and serotonergic measurements in rodents.

Preclinical Findings: Rodent Tissue and Gene Expression

A rodent pMCAO study used genome-wide expression profiling (Illumina RatRef-12 BeadChip) to examine cortical tissue (PMC3987924).

In that rodent dataset, immunoglobulin genes were among the most strongly upregulated transcripts. Genes associated with vascular processes and intracellular calcium signaling also showed expression changes.

Rodent studies also examined behavioral endpoints. The specific task and measured endpoint matter when comparing those reports.

Transcriptomic Depth

In rat hippocampal tissue without induced ischemia, Semax-associated expression changes were reported for MAPK10, APP (amyloid precursor protein), and fibronectin 1. These were gene-expression measurements in that animal model.

Separate articles discuss DSIP and Pinealon. Those peptides have different sequences from Semax.

Semax vs. Selank: Same Lab, Different Compounds

Semax and Selank are heptapeptides developed at the same institute. Both contain a C-terminal Pro-Gly-Pro segment, but their full sequences differ.

Parameter	Semax	Selank
Parent	ACTH residues 4 to 10	Tuftsin
Sequence	MEHFPGP	TKPRPGP
Research Topics	GABA-related signaling and gene expression
Reported Research Endpoints	Rat tissue studies: BDNF/NGF expression and dopamine/serotonin measurements	GABAA modulation, enkephalinase inhibition
BDNF Measurements	Reported rat measurements: 1.4-fold protein and threefold mRNA changes	No model-specific BDNF measurement is given here
Behavioral Study Context	Task, comparator, and observation time are not specified here
C-terminal Segment	Pro-Gly-Pro	Pro-Gly-Pro
Gene Expression	Frontal-cortex gene-expression profiling; model details are not specified here

The clearest distinction is structural: Semax is ACTH-derived, while Selank is tuftsin-derived. Their molecular findings come from different experiments and should not be treated as interchangeable.

Assay Context and Analytical Controls

The experiments described above used different endpoints, including peptide binding, gene expression, and protein measurements. Each result needs the corresponding model and assay conditions.

Laboratory assay notes:

• The ACTH-derived segment and the Pro-Gly-Pro tail are distinct sequence features to consider when selecting peptide comparators
• Binding is calcium-dependent. Control for that in your in vitro work or you’ll get artifacts
• Rat tissue studies reported region-specific BDNF responses. Keep brain region and collection time consistent when comparing samples
• PGP tail makes Semax resistant to aminopeptidases. That changes your PK modeling assumptions

Analytical characterization can include HPLC purity measurements and mass spectrometry for peptide identity. Aggregation and impurities can affect assay interpretation.

Comparing Peptide Sequences

Chemical comparisons can start with the sequences: Semax is MEHFPGP, while Selank is TKPRPGP. Both contain a C-terminal Pro-Gly-Pro segment.

Conclusion

The cited studies reported nanomolar binding measurements in rat tissue preparations and region-specific gene-expression observations in rodents. Binding and expression results describe different experimental endpoints.

The molecular identity of the binding site remains unresolved, despite a reported K_D of 2.4 nM in rat basal forebrain preparations. Comparisons with Selank need to account for differences in sequence and assay conditions.

There’s a lot of open territory here. For neuroscience labs with the right tools, Semax is one of the more interesting compounds to put under the microscope.

For laboratory and research use only. Not for human consumption.

References

1. Dolotov OV, et al. Brain Res. 2006;1117(1):54-60. PMID: 16996037
2. Dergunova LV, et al. BMC Genomics. 2014;15:228. PMC3987924
3. Filippenkov IB, et al. Novel Insights into the Protective Properties of ACTH(4-7)PGP (Semax) Peptide at the Transcriptome Level Following Cerebral Ischaemia-Reperfusion in Rats. Genes. 2020. PMC7555804
4. Dolotov OV, et al. J Neurochem. 2006;97 Suppl 1:82-86.
5. Eremin KO, et al. Semax, An ACTH(4-10) Analogue with Nootropic Properties, Activates Dopaminergic and Serotoninergic Brain Systems in Rodents. Neurochem Res. 2005;30:1493-1500.
6. Dolotov OV, et al. The heptapeptide SEMAX stimulates BDNF expression in different areas of the rat brain in vivo. Doklady Biol Sci. 2004;399:478-481.
7. Filippenkov IB, et al. Brain Protein Expression Profile Confirms the Protective Effect of the ACTH(4-7)PGP Peptide (Semax) in a Rat Model of Cerebral Ischemia-Reperfusion. Int J Mol Sci. 2021.
8. Agapova TY, et al. Semax and Pro-Gly-Pro Activate the Transcription of Neurotrophins and Their Receptor Genes after Cerebral Ischemia. Cell Mol Neurobiol. 2009. PMC11498467
9. Ashmarin IP, et al. A nootropic adrenocorticotropin analog 4-10-semax (15 years experience in its design and study). Zh Vyssh Nerv Deiat. 1997;47(2):420-430.