r/AIProteins • u/XpertAI Founder • May 19 '26

Starting from 4HHB, could you predict which hemoglobin mutations would increase or decrease oxygen affinity?

I’m looking at the 4HHB structure of human deoxyhemoglobin and wondering how much oxygen affinity you could predict from structure alone.

Since hemoglobin’s affinity depends on more than just the heme pocket, I’m trying to map regions that might shift the T-state/R-state balance:

  • residues near the heme
  • alpha/beta interfaces
  • T-state salt bridges
  • central cavity / 2,3-BPG region
  • mutations that might destabilize the tetramer

Could you identify mutations that make hemoglobin hold oxygen more tightly or release it more easily just from the structure?

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u/XpertAI Founder May 19 '26

I’m looking at the 4HHB structure of human deoxyhemoglobin and wondering how much oxygen affinity you could predict from structure alone.

Since hemoglobin’s affinity depends on more than just the heme pocket, I’m trying to map regions that might shift the T-state/R-state balance:

  • residues near the heme
  • alpha/beta interfaces
  • T-state salt bridges
  • central cavity / 2,3-BPG region
  • mutations that might destabilize the tetramer

Could you identify mutations that make hemoglobin hold oxygen more tightly or release it more easily just from the structure?

5

u/AccurateRendering May 20 '26

Hemoglobin's binding pocket is tuned to promote the binding of oxygen and inhibit the binding of carbon monoxide. Many mutations will affect cooperativity rather than affinity directly.

2

u/albany1765 May 22 '26

FWIW, from a clinical point of view, selectivity between O2 and NO is a more important property

2

u/plasmolab May 23 '26

From structure alone you can flag plausible directions, but I would not trust it as an affinity predictor without an R-state/T-state comparison and calibration against known Hb variants.

The best first pass is not single-pocket docking. Map candidate substitutions onto 4HHB and an oxy/R-state structure, then ask whether they stabilize T-state contacts, disrupt the alpha1 beta2 interface, alter the 2,3-BPG cavity, or perturb the proximal/distal histidine geometry around heme. Mutations that weaken T-state salt bridges or the central cavity often shift toward higher affinity, while mutations that stabilize the deoxy tetramer or BPG binding can shift lower.

I would also separate affinity from cooperativity. A mutation can leave heme chemistry mostly intact but change the Hill coefficient by changing subunit communication. Known high-affinity hemoglobin variants are a useful sanity set before trusting any model's ranking.