Phosphoproteomics elucidates the functional impact of the PTPN11 p.Asn308Ser variant in a Noonan syndrome pedigree.

Noonan syndrome (NS) is a common autosomal dominant disorder with considerable clinical heterogeneity. Mutations in the PTPN11 gene, encoding the SHP2 protein, constitute the most prevalent genetic cause of NS. Genetic sequencing of a pedigree exhibiting typical facial dysmorphism and short stature identified the same heterozygous PTPN11 variant (NM_001330437.2: c.923 A > G, p.Asn308Ser) in all seven affected individuals, co-segregating with the phenotype. Using a multi-level approach that integrated experimental structural analysis, molecular dynamics simulations, protein-protein interaction network analysis, quantitative phosphoproteomics, and functional validation in cellular models, we systematically elucidated the pathogenic mechanism of the p.Asn308Ser mutation. This revealed that the mutation disrupts critical hydrogen bonds and remodels the interaction network. This change enhances conformational heterogeneity and shifts the protein into an activated "open" state. Consequently, the mutation strengthens interactions with hub proteins, such as GRB2 and SRC, resulting in sustained RAS/MAPK activation. Phosphoproteomic analysis showed that the mutation induces extensive phosphorylation events, with differentially phosphorylated proteins significantly enriched in the nucleus, particularly in pathways related to chromatin organization and ATP-dependent chromatin remodeling. Further functional validation indicated that aberrantly activated ERK may phosphorylate chromatin remodeling complexes such as SWI/SNF, thereby directly connecting cytoplasmic signaling to aberrant epigenetic regulation in the nucleus. This study delineates the complete pathogenic axis of the PTPN11 p.Asn308Ser mutation, spanning atomic conformational changes and sustained signaling activation to aberrant nuclear chromatin remodeling. These findings extend the understanding of NS pathophysiology to the epigenetic level and provide a theoretical foundation for future interventions targeting both signaling pathways and chromatin states.