Dermorphin vs TB-500

Dermorphin

Dermorphin is a seven-residue opioid peptide first found in the skin secretions of South American frogs of the genus Phyllomedusa. Its second residue is D-alanine. Ribosomes incorporate only L-amino acids, so this residue arises by conversion of an ordinary L-amino acid after the peptide chain is made; dermorphin was among the first natural peptides in which this was shown, which gives it a place in peptide biochemistry beyond opioid research. Work on it has been largely pharmacological, using receptor-binding assays, isolated tissue preparations and animal models. It and its synthetic analogues serve as reference ligands for one opioid receptor type. Human data are minimal.

TB-500

TB-500 is a synthetic seven-residue peptide, Ac-LKKTETQ, matching residues 17 to 23 of the 43-residue actin-binding protein thymosin β4. The stretch it copies lies in the central actin-binding region of thymosin β4; the N-terminal acetyl cap is a synthetic addition, since that position is internal in the native protein. The name is sometimes applied loosely to full-length thymosin β4, and the two should be kept apart: they differ in length, in mass (about 0.9 kDa against about 5 kDa) and in which parts of the parent protein they contain. Most published research concerns the full-length protein, examined in cell culture and in rodent models of skin, cardiac and corneal injury. Work on the fragment alone is far thinner, and it cannot be assumed to share the properties described for the whole protein.

How Dermorphin acts

Dermorphin has been reported to bind the mu-opioid receptor with high selectivity over the delta and kappa types. The mu receptor is a G protein-coupled receptor linked to Gi/o proteins; its activation inhibits adenylyl cyclase, opens inwardly rectifying potassium channels and closes voltage-gated calcium channels, which lowers neuronal excitability and transmitter release. Structure–activity work has focused on the N-terminal Tyr-D-Ala sequence, which is shared with other amphibian opioid peptides such as the deltorphins, and on how the D-residue slows breakdown by peptidases compared with the all-L form. Much of the literature uses dermorphin analogues as tools for mapping mu-receptor pharmacology.

How TB-500 acts

Full-length thymosin β4 binds monomeric G-actin in a one-to-one complex and is a major actin-sequestering protein in many cell types, holding actin in unpolymerised form. Structural studies place the LKKTET motif, shared with the WH2 family of actin-binding domains, at the centre of that contact, flanked by N-terminal and C-terminal segments that also touch actin. A small number of cell studies have reported that the isolated fragment affects endothelial cell migration, but how closely it reproduces the actin binding of the whole protein is not well established. Other activities attributed to thymosin β4 map elsewhere: the N-terminal tetrapeptide Ac-SDKP is released by enzymatic cleavage and has been studied separately.

The records side by side

• Type: Dermorphin, Heptapeptide; TB-500, Heptapeptide (thymosin β4 fragment)
• Length: Dermorphin, 7 amino acids; TB-500, 7 amino acids
• Molecular weight: Dermorphin, 802.9 g/mol; TB-500, 889.0 g/mol
• Molecular formula: Dermorphin, C40H50N8O10; TB-500, C38H68N10O14

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.