Science1 publisher2 min readPublished
A nitrogenase pulled from a vent archaeon makes ammonia only above 90 C
Tristan Wagner's lab at the Max Planck Institute for Marine Microbiology purified the enzyme straight from Methanocaldococcus infernus and got the simplest nitrogenase structure solved so far, with features of all three families.
The Scientist · Science desk
What happened
- Researchers in Tristan Wagner's laboratory at the Max Planck Institute for Marine Microbiology in Bremen grew the deep-sea archaeon Methanocaldococcus infernus and got it to fix nitrogen gas above 90 C.
- The nitrogenase they purified from the organism only began to break apart at 90 C, and some of it was still intact at 98 C.
- They crystallized the enzyme and took it to the synchrotron at the Institut de Biologie Structurale in Grenoble, which gave a structure at near-atomic resolution.
- That structure is the simplest nitrogenase studied so far, and it combines features of all three major families: molybdenum, vanadium and iron-only.
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Why it matters
- capability A protein that holds together to 98 C can be held in states that decay too fast to see in ordinary nitrogenase preparations. That is the payoff Maslac named for work on the mechanism.
- constraint Checking this result needs oxygen-free culture, purification and crystallography end to end, so the set of labs that can attempt a replication is small.
- precedent If the archaeal enzyme is nearest the ancestral form, mechanistic chemistry gets a new reference system, and the burden shifts to phylogenetics to show the lineage runs that way.
- constraint Any biotechnology built on this enzyme inherits its heat requirement, since it makes ammonia only when hot; the institute offers cleaner fertilizer production as something the work could eventually inspire.
The enzyme holds its reaction states long enough to study them. Nevena Maslac, the first author, said the enzyme "is not active at room temperature. Rather, we show that it only produces ammonia at high temperatures. Its extreme stability allowed us to study states of the nitrogenase that are usually difficult to capture." [9] Activity has to be measured hot, and the protein sits idle through room-temperature handling. [18] Maslac also said the enzyme "is designed to function under conditions in which most proteins would rapidly decay, like egg white cooked in hot water". [8]
The hard part is the chemistry: nitrogen is about 78 percent of the atmosphere and unusable to plants and animals because a triple bond joins the two atoms of N2. [1] M. infernus lives in volcanic marine environments where vent fluids can exceed the boiling point of water. [2]
The enzyme works at the very top of its own stability range. The organism fixes N2 above 90 C, and 90 C is also where the purified protein starts to break apart. [3][7][20] Eight degrees separate that onset from the last trace of folded enzyme at 98 C. [19] The institute's announcement calls that last trace only "some", and mentions a newly observed reaction state without naming it. [17]
Wagner said the enzyme "seems to share traits of the molybdenum, vanadium, and iron forms" and that "this type of nitrogenase could be similar to a common nitrogenase ancestor, the ancient system all of them evolved from". [6] The institute says the combination of features supports the possibility that ancient nitrogenases resembled this archaeal enzyme more closely than the nitrogenases found in bacteria today. [14] Mixed traits are consistent with an ancestral form and equally consistent with a simplified descendant that shed parts. Ordering the lineage takes sequence comparison across the three families, and the institute's own word for the ancestral reading is "possibility". [14]
Oxygen permanently damages nitrogenase metallocofactors, so every step ran under strictly oxygen-free conditions. [10] The work combined microbial physiology, native enzyme purification, biochemistry and structural biology. [11] Nitrogenase carries what the institute calls the most complex metallocofactor known in biology, and the molybdenum versions are still both the most studied and the highest-performing. [4][5]
What to watch
- The peer-reviewed paper: which reaction state was newly observed, and at what resolution in angstroms the structure was refined.
- An ammonia production rate for the archaeal enzyme measured at its working temperature, next to a molybdenum nitrogenase run under its own optimum.
- Sequence and phylogenetic analysis testing whether this enzyme sits near the root of the three families or is a simplified descendant.