The phosphate tail of ATP binds the p-loop motif, evolutionary conserved, going back to since forever. In the dominant model, the deprotonated hydroxyl groups are complexed with Mg2+, at least two of them.
I was wondering about a hypothetical model (could consider it "fantasy" or just thought experiment, without disclosing if there is any actual credible reason to think about it. )
If the three deprotonated hydroxyl groups were actually protonated, is there still a fit in the p-loop? This would remove the Mg2+, since it is substituted by H+, charge-wise.
That ATP does not actually get protonated like that in the dominant models, is neglected in the question. I am just wondering about fit in the p-loop. To have a way to think of that, imagine the ATP might be slightly modified, or some other input altered, but the p-loop itself is the same, and the phosphate tail except here it is fully protonated.