Science1 publisher2 min readPublished
A CU Anschutz protein map finds red blood cells rewiring a third of their contacts under low oxygen
The Blood paper counts 3,775 proteins in ultra-pure mature human red cells and reports a third of their physical interactions rearranging when oxygen falls, with the causal test run in animals missing part of Band 3.
The Scientist · Science desk
What happened
- University of Colorado Anschutz researchers reported 3,775 proteins in ultra-pure mature human red blood cells in the journal Blood, more than triple the estimates published 15 years ago.
- The team also mapped thousands of physical interactions between those proteins, and nearly a third of the mapped interactions were remodeled when oxygen levels dropped.
- The map included a previously unknown interaction between biliverdin reductase B and Band 3, linking changes at the membrane to the metabolic machinery inside the cell.
- Animals engineered without the oxygen-responsive N-terminal region of Band 3 had red cells that could not mount the normal metabolic response to low oxygen, and their exercise capacity was impaired.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- capability Hypoxia research that could previously only describe 2,3-BPG rising now has two specific things to perturb: the oxygen-responsive end of Band 3 and the BLVRB relay that carries a nitric oxide signal to the enzyme setting 2,3-BPG synthesis.
- constraint The human-relevance argument rests on exercise capacity in animals, so anything asserted about athletes or altitude acclimatization stays an extrapolation until someone samples people.
- decision A cell that cannot synthesize new protein forces a methods choice on anyone studying it under stress: measuring abundance will miss the regulation, and only interaction mapping will see it.
A cell without a nucleus has no transcriptional option. It cannot answer falling oxygen by making a new protein, so it works with the inventory on hand [20]. Under low oxygen that inventory gets rearranged. Binding between Band 3, the most abundant protein in the red cell membrane, and deoxygenated hemoglobin rose about threefold [6][8]. Glucose handling shifted at the same time and production of 2,3-BPG went up [7]. 2,3-BPG loosens hemoglobin's hold on oxygen, so more of it comes off in tissue [7].
"What we are seeing is a cell that adapts without making new proteins," said Angelo D'Alessandro, the study's senior author and a professor of biochemistry and molecular genetics at CU Anschutz [17][16]. "Protein interactions become a form of rapid biological regulation" [17].
Interactions that rearrange as oxygen falls is a correlation. The deletion experiment is the test of requirement, and it was run in animals [12]. Its readout was exercise capacity. The authors did not study athletes or people acclimatizing to altitude [13]. Earlier work had already shown that human red cells raise 2,3-BPG during high-altitude exposure [14]; this paper identifies part of the machinery that may coordinate that response [15].
3,775 is more than triple the estimates of 15 years ago [1]. That puts the older lists below roughly 1,258 [19]. Over those 15 years purification protocols and instrument sensitivity both changed while the cell stayed the same, so how much of the increase belongs to each is a question a total count leaves open. The one-third figure sits on the same footing: it is a fraction of a map the paper describes as thousands of interactions [5][2].
Red cells are nearly 83% of the cells in a human body [3], and the authors place the findings in high-altitude exposure, strenuous exercise, and the severe loss of oxygen delivery that can follow trauma and hemorrhagic shock [4].
BLVRB's job in the model is relay. It transfers a nitric oxide-derived chemical signal to another enzyme that immediately regulates 2,3-BPG synthesis [10]. That connects the state of the membrane to how the cell spends glucose. Plants independently evolved essentially the same switch, using it to make molecules that regulate photosynthesis [11]. "It is striking to see the same basic chemical strategy used across such distant forms of life," D'Alessandro said [18].
What to watch
- The same interaction map measured in blood drawn from people at altitude, or from patients in hemorrhagic shock.
- Independent labs reproducing the 3,775-protein count with their own purification protocol and instruments.
- Any compound acting on the Band 3 to BLVRB link that changes 2,3-BPG in a hypoxic animal.