Protein language models such as ESM-2 learn rich residue representations that achieve strong performance on protein function prediction, but their features remain difficult to interpret as structural
& evolutionary signals are encoded in dense latent spaces. We propose a plug-
&-play framework that projects ESM-2 representations onto protein contact graphs
& applies
SoftBlobGIN, a lightweight Graph Isomorphism Network with differentiable Gumbel-softmax substructure pooling, to perform structure-aware message passing
& learn coarse functional substructures for downstream prediction tasks. Across enzyme classification, SoftBlobGIN achieves 92.8% accuracy
& 0.898 macro-F1. Unlike post hoc analysis of protein language models alone, our method produces directly auditable structural explanations: GNNExplainer recovers biologically meaningful active-site residues, spatially localized functional clusters,
& catalytic contact patterns. On binding-site detection, SoftBlobGIN improves residue AUROC from
0.885 using an ESM-2 linear probe to
0.983, indicating that these structural explanations are not recoverable from language-model features alone. Learned blob partitions provide an additional layer of interpretability by automatically grouping residues into functional substructures, with blobs containing annotated active-site residues showing
1.85× higher importance than other blobs (
ρ=0.339,
p=0.009), without any active-site supervision. Our framework requires no retraining of the language model, adds only
∼1.1M parameters,
& generalises across ProteinShake tasks, achieving
Fmax of
0.733 on Gene Ontology prediction
& AUROC of
0.969 on binding-site detection. We position this as an interpretable structural companion to protein language models that makes their predictions more transparent
& auditable.