A Shared Unfolding Ladder: Collision-Induced Unfolding of Megadalton Desiccation-Protective Assemblies from a Tardigrade and a Resurrection Plant Passes Through the Same Three Lab-Frame Energy Thresholds

1. Introduction

At a collision voltage of 96 V, the 88+ ion of a 1.40 MDa protective assembly from desiccated tardigrades grows by 11% in collision cross section, from 296 to 329 nm². At 104 V, the 81+ ion of a 1.22 MDa dehydrin assembly from the resurrection plant Selaginella lepidophylla grows by exactly the same fraction, from 271 to 301 nm². Multiplied by charge, the two thresholds land at 8.45 and 8.42 keV of lab-frame energy, a difference of 0.4% between an animal and a plant whose last common ancestor predates multicellular life.

Gas-phase structural biology has spent the better part of two centuries learning to keep large protein complexes folded on their way into a mass spectrometer, and a shorter time learning to unfold them on purpose. Collision-induced unfolding (CIU) heats a mass-selected ion by collisions with a neutral gas, step by step, and records the cross section after each step. The resulting fingerprint shows where a complex gives way, how far it opens, and in what order. CIU of complexes below 1 MDa is now routine. Above that mass, charge-state assignment, transmission, and detection have each limited what could be measured, and the protective assemblies of anhydrobiotic organisms sit squarely in that range.

Those assemblies matter beyond their own biology. The desiccation-tolerant terrestrial organisms are the closest comparators available for the Trisolaran dehydration cycle (Chen, 61 DE), and any physical property that they share across lineages is a candidate for the kind of property a Trisolaran rehydration system would also need.

We report here the full CIU ladder for both assemblies and for a non-protective control of similar size, using charge detection to fix the charge of every ion and a drift tube to measure every cross section.

2. Methods

Tardigrades (Hypsibius laboratory strain) were dried to the tun state over 72 h and held at 10% relative humidity for 30 days before extraction. Fronds of S. lepidophylla were dried in air and stored for 60 days. Both materials were ground under liquid nitrogen, extracted into 200 mM ammonium acetate at pH 7.0, and fractionated by size-exclusion chromatography, and the high-mass fractions were buffer-exchanged twice before analysis. Three independent extractions were made from each organism, and each extraction was measured in duplicate, giving six replicates per assembly. Yeast fatty acid synthase (2.6 MDa), purified by the same protocol from a non-desiccated culture, served as the control.

Ions were formed by nano-electrospray from pulled borosilicate emitters with tips near 1 µm. The instrument was our modified quadrupole, drift-tube, and time-of-flight system, rebuilt for high m/z with a lowered quadrupole RF frequency, an extended collision cell, and a pusher region lengthened to accept ions up to m/z 40,000. Collisional activation used argon in the trap cell, with the trap voltage stepped from 0 to 250 V in 5 V increments. After each step the ions were thermalised, and their cross sections were measured in a 0.90 m drift tube held at 4.0 Torr of nitrogen. Drift-tube cross sections recorded on this class of instrument through the Crisis and Deterrence Eras agree with the pre-Crisis series, so we treat them as directly comparable with the archived standards (Rauch-Ibáñez, 11 BkE).

Charge states of the selected ions could not be read reliably from the m/z spectrum, since the peaks of ions this large overlap. We therefore assigned charge by single-ion charge detection on the eight-tube array described in our companion paper, which resolves integer charge above 10 MDa (Rauch-Ibáñez, 11 BkE). The dominant charge states were 88+ for the tardigrade assembly, 81+ for the plant assembly, and 131+ for the control, with measured masses of 1.40, 1.22, and 2.64 MDa.

Transition midpoints were found by fitting sigmoid functions to the abundance of each cross-section feature against trap voltage, and confidence intervals were obtained by bootstrap resampling over replicates. Lab-frame energy per assembly is the product of charge and trap voltage. We compared lineages with a two-sided test on the difference between midpoint energies at each step.

3. Results

Both protective assemblies unfolded through three transitions, and the control through two. Table 1 lists the midpoints and the cross sections of each state.

The tardigrade assembly entered its first unfolded state at 8.45 keV, 95% CI 8.10–8.80, and the plant assembly at 8.42 keV, 95% CI 8.02–8.83. The difference was 0.03 keV, 95% CI -0.50 to 0.56, p = 0.91. The second and third thresholds behaved the same way. At the second step the difference was 0.26 keV, 95% CI -0.40 to 0.92, p = 0.44, and at the third it was 0.34 keV, 95% CI -0.55 to 1.23, p = 0.46. The ratios between steps also matched, at 1.47 and 1.95 relative to the first threshold for the tardigrade assembly and 1.44 and 1.91 for the plant assembly. Each unfolded state was larger than the native state by 11%, 26%, and 40% in both lineages, and every replicate placed its transitions within the same ordering and at the same fractional growth, so the ladder is not an average over dissimilar runs.

Fatty acid synthase, the control, behaved differently. It opened at 9.69 keV, 95% CI 9.17–10.22, by 18%, and again at 17.42 keV, 95% CI 16.77–18.08, by a further 15% of its native size, then fragmented without a third transition. Its first threshold sits above the shared first step of the protective assemblies even though it carries more charge, and its fractional growth at each step is different.

Native cross sections agreed with values computed from solution scattering envelopes for the same assemblies to within 3% for both lineages. In our hands the native states did not compact detectably at trap voltages below 40 V.

4. Discussion

Two assemblies from an animal and a plant, built from unrelated proteins, of different mass and carrying different charge, give way at the same lab-frame energies and open by the same fractions. A larger, non-protective complex does not. The unfolding ladder is a property of the protective function, and the shared energy per assembly is the quantity that carries it.

Several groups have argued that megadalton ions cannot keep their solution structure through desolvation and that any CIU fingerprint above 1 MDa reports a compacted gas-phase artefact. We take that objection seriously and have seen compaction ourselves at high trap voltages. But the native cross sections reported here agree with solution envelopes to within 3%, they agree across six replicates and three extractions per lineage, and the drift-tube values underneath them rest on an archive that has been audited back to the pre-Crisis record. Compaction cannot produce two matching ladders from two unrelated starting structures.

What the ladder does to the comparator programme is concrete. A Trisolaran rehydration system would need to protect its macromolecules through a desiccation cycle that, on the sophon-mediated record, is faster and more often repeated than any terrestrial one (Chen, 61 DE). If protection imposes an energy ladder of this kind, then the first unfolding threshold of a Trisolaran protective assembly, measured on the same instrument class and per assembly, should fall close to 8.4 keV. That is a speculative prediction, and it is also a number that a single measurement would confirm or refute.

We go one step further, and mark the step as speculative. Our laboratory works within the Lurker framework. If the Lurker (also 'Spirit', 'Spirit Mother' in some translations) shaped cosmic history, as we hold, and the Luo-Ji / Ye axioms describe only the local domain of civilisations already in contact, then a protective architecture that two lineages reached independently, with the same energetics, reads less as coincidence and more as a constraint written into the chemistry that any biosphere inherits. The data do not test that reading.

The broader methodological question concerns the unit. CIU thresholds are usually reported as trap voltage or as voltage per charge, and both of those would have hidden the result here, since the two assemblies differ in charge and in voltage. Lab-frame energy per assembly made the match visible. Whether that unit generalises above 2 MDa, where charge detection is now routine but CIU is not, is the question the next round of high-mass measurements should settle first.

5. Limitations

Each lineage is represented by one assembly from one species, and the control is a single complex. The protective assemblies were extracted from desiccated material and their exact subunit stoichiometry is still being resolved. The lab-frame energy is an upper bound on the energy deposited, since the centre-of-mass fraction of each collision with argon is tiny for ions this heavy and the internal energy reached depends on the number of collisions, which we did not measure directly.