PTD-DBM

What PTD-DBM is, structurally

PTD-DBM is a single peptide made of two joined segments, and its name abbreviates both: a protein transduction domain, and a Dishevelled-binding motif corresponding to a short region of the human protein CXXC5. The vial holds one continuous chain, not a mixture of two peptides. What either segment is for belongs to the research article.

Two specification fields are empty at source, and both can be filled from the public record. The deposited record for this CAS gives C124H225N61O28S2, which computes to 3082.64, exactly the weight the product page states. It resolves to twenty-five residues that regenerate the formula exactly. The sections below are built on it, with that origin stated plainly.

Read that way, the composition is extreme. Thirteen side chains carry a strongly basic group, ten of them arginine guanidines, and not one is acidic; the only ionisable acid is the C-terminal carboxylate. The molecule is cationic across the whole practical pH range, with no isoelectric point to pass through. Ten arginines also make it very hydrophilic, so dissolving it is not the difficulty.

The join is a run of four glycines, an ordinary peptide bond no more labile than the rest of the backbone. What distinguishes it is the consequence of a break rather than its likelihood: hydrolysis there gives pieces of roughly 1496 and 1605, each near half the parent mass.

Two sulfurs are exactly the number an intramolecular bridge requires, and the deposited record draws both as free thiols. Whether the supplied material is still reduced that record cannot settle, so handle it as though the thiols are open, a precaution costing nothing either way.

Reconstitution and handling

Sterile water is the default solvent and should take this material up readily. Add diluent down the inside wall of the vial, swirl rather than vortex, and let the solution clarify.

The difficulty is not dissolving the powder but keeping what dissolved. A molecule this positively charged binds avidly to any negatively charged surface: borosilicate glass is a poor choice, its silanols being ionised above roughly pH 3, and low-protein-binding polypropylene is the better default. Adsorptive loss is a general peptide risk, but here one of degree rather than trace: at low concentration the share lost to the vessel can be substantial.

Sterile filtration deserves the same caution: cellulose acetate and other common membranes carry a net negative charge and can deplete a cationic peptide appreciably in one pass. A low-binding membrane and a discarded first fraction are the usual mitigations.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C or below, sealed, desiccated and protected from light, and let a cold vial warm before opening so moisture does not condense on it. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thaw one vial repeatedly.

The thiols dominate stability in solution. Dissolved oxygen oxidises them slowly at neutral pH and faster as pH rises, and trace metals catalyse it, so a near-neutral solution in a clean vessel is the milder condition. The dry solid is far better protected, and desiccation matters because material this charged is hygroscopic.

These are storage conditions for the material, not dosing or administration guidance.

How PTD-DBM is tested

Reversed-phase HPLC establishes chromatographic purity as area percent, and this molecule is awkward on a standard C18 column. With thirteen basic side chains and no hydrophobic block, it retains poorly and elutes early unless the mobile phase supplies an ion-pairing agent, trifluoroacetic acid being the usual choice. An unadapted method can return a flattering figure because nothing was resolved.

Area percent is not peptide content by weight, and the gap is unusually wide here. Each basic site can carry a trifluoroacetate counter-ion: roughly 1480 mass units of salt against 3083 of peptide, close to a third of the gross weight. The product page states the labelled quantity as net peptide content.

Mass spectrometry confirms identity. The average mass is 3082.64 and the monoisotopic 3080.75, and with 124 carbons the monoisotopic peak is not the tallest in the envelope, so establish which basis is reported before reading a difference as modification. A species two units below the average is the closed bridge, not a separate impurity.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

No molecular formula is given on the product page. Is one known? The deposited record for this CAS gives C124H225N61O28S2, which computes to 3082.64, reproducing the stated weight exactly, so that figure appears formula-derived. The formula is not carried in the product database.

Why does this peptide need an ion-pairing agent to run properly? It carries thirteen basic side chains and no acidic ones, so at the acidic pH of a reversed-phase gradient it is close to fully protonated, with little to bind a C18 surface. Ion pairing masks that charge and restores retention.

Full specifications for PTD-DBM.