Activation-loop phosphorylation is a demanding test of protein-structure prediction because it modulates both local chemistry and the relative occupancy of pre-existing kinase conformations. This critical narrative review asks whether explicit phosphoresidue representation allows AlphaFold-based approaches to capture phosphorylation-induced conformational change. Targeted searches of PubMed and official publisher databases incorporated structural, solution-biophysical, biochemical and computational evidence. Extracellular signal-regulated kinase 2 (ERK2) indicates that phosphate-stabilised contacts coexist with activation-loop motion, whereas Aurora A shows that phosphorylation can induce strong activation without a coarse aspartate–phenylalanine–glycine (DFG)-out-to-DFG-in population shift. These cases make the required prediction target a condition-dependent ensemble rather than a single phosphorylated structure. AlphaFold 2-derived multiple-sequence-alignment perturbations broaden state coverage, and AlphaFold 3 can encode modified residues, ligands and ions. However, a 109-protein benchmark showed only a small, statistically non-significant improvement in phosphorylated-state alignment when phosphorylation was supplied explicitly. Current AlphaFold models can therefore produce chemically informed candidate states, but their output frequencies are not calibrated solution populations. A four-level validation framework is proposed to separate local chemistry, state recovery, perturbation-induced population shifts and prospective functional prediction. Ensemble-sensitive validation remains necessary, while physical reweighting can help explain phosphorylation-dependent kinase regulation.
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Ziyao Wang (2026) studied this question.