IGF-1 LR3: structure and analysis

What it is

IGF-1 LR3 is a recombinant analog of insulin-like growth factor 1, modified by a 13-amino-acid N-terminal extension and a single substitution at position 3. Native IGF-1 is a 70-residue protein, so the extended analog is a genuine protein rather than a short peptide.

That makes it the largest and structurally most complex molecule in this catalogue by a wide margin, and the only one produced recombinantly rather than by chemical synthesis.

As a protein it has a folded three-dimensional structure stabilised by internal disulfide bonds, which a short synthetic sequence does not have and cannot lose.

How it is produced

Produced recombinantly rather than by chemical synthesis: the sequence is expressed in a biological system, then recovered, purified and lyophilized. This is a materially different process from solid-phase synthesis, and it changes which impurities are plausible and which analytical methods are appropriate.

Aggregation and misfolding become relevant impurity classes in a way they are not for a short synthetic sequence, and residual host-derived material — including endotoxin, where expression is bacterial — becomes a parameter worth screening.

Confirming identity

Mass spectrometry confirms the expected mass including the N-terminal extension and the position-3 substitution. For a molecule of this size, high-resolution measurement is required to resolve the intended species from closely related variants.

Disulfide bond arrangement is part of identity for this compound in a way it is not for anything else here. A correctly sequenced protein with incorrectly paired disulfides has the same molecular mass and is not the same molecule, so mass alone is not a complete identity confirmation.

Analytical considerations

The relevant impurity classes are different from a synthetic peptide's. Aggregation — molecules associating into dimers and higher species — is a real concern for proteins and is invisible to a reversed-phase purity method designed to separate synthesis by-products. Size-exclusion chromatography reports what reversed-phase cannot see.

Because expression is biological, host-derived material is a plausible contaminant. Endotoxin screening is materially more relevant for this compound than for a synthetically assembled peptide, where there is no expression system for it to originate in.

Misfolded and partially reduced species are additional classes with no analogue in solid-phase synthesis. A certificate for a recombinant protein that reports only reversed-phase purity has not addressed the questions specific to how it was made.

What its certificate reports

A certificate for a lot of this material names the lot, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a lot, not to a product line. When a new lot is released it is tested again, and the certificate published against it is that lot's certificate — a previous lot's result is never carried forward.

Research use only

This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.