Does deamidation dominate for survodutide held at minus 80 °C?

The particulars: deamidation · survodutide · minus 80 °C.

I would like the mechanism, because I want to be able to reason about the cases nobody has written about.

I have tried to reason it out from first principles and got to two contradictory conclusions.

So what is the mechanism, and how well established is it?

At minus 80 °C the question is which route is fastest, not whether deamidation happens — and the routes do not share an activation energy, so their ranking changes with temperature. minus 80 °C is 85 kelvin below a refrigerator, and below the glass transition of a lyophilised cake the ten-degree rule of thumb stops applying at all — solid-state chemistry is not slow liquid chemistry, it is a different regime, and the failure modes that survive it are mechanical rather than chemical. That multiplier is an average over every route at once, which is exactly why it cannot tell you which one wins. Asn and Gln lose the amide through a succinimide intermediate, so the product is one dalton heavier and usually resolves as a shoulder on the main peak rather than as a peak of its own. So the way to answer it for your vial is to pick the method that sees deamidation specifically and run it against a control held cold, rather than to infer a mechanism from a purity number that averages all of them.

The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.

Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.

Degradation pathway by condition

Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.

Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.

At dilute concentrations, suspect adsorption before you suspect chemistry.

Answering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.

Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.

It helps to be literal here: freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.

Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

edited 21 Dec 2024 by b_delacroix — added the method parameters

Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.

Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.

Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.

Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.

Cold, dry, dark, still. Those four words cover most of the mitigation.

The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.

Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Sequence determines which pathways apply, so general statements are general.

Sequence decides which pathways are even available. Check the residues.