PPFIA2

PPFIA2 (Liprin-α2) is a multidomain scaffold protein that engages the cytoskeletal adaptor GIT1: a single α-helix on liprin-α binds the paxillin-binding domain of GIT1 in a manner structurally distinct from the GIT1–paxillin LD4 interaction, and GIT1 variants that disrupt this contact impair focal adhesion assembly, placing the liprin-α–GIT1 interaction in focal adhesion dynamics (PMID:30737283). Beyond this validated interaction, the broader domain architecture of PPFIA2 has been characterized only computationally, with SAM1–SAM3 predicted to bind LAR-subfamily protein tyrosine phosphatases and Liprin-β (PPFIBP) proteins, PFIH2–PFIH3 predicted to bind KIF1A, and a C-terminal VRTYSC motif predicted to bind GRIP proteins (PMID:14612982). PPFIA2 protein is expressed at synapses, where its levels decline upon perturbation of the SNARE release machinery (PMID:40181518), and de novo heterozygous PPFIA2 variants are associated with a neurodevelopmental disorder (PMID:41044885). No direct experimental dissection of PPFIA2's synaptic scaffolding mechanism is available in the corpus.

1. 2003 Low

   Established a domain-level map of PPFIA2, defining which regions are predicted to mediate its protein interactions and framing it as a multidomain scaffold.

   Evidence Comparative sequence/domain architecture analysis across PPFIA paralogs in silico

   PMID:14612982

   Open questions at the time

   • Purely computational — no experimental validation of any predicted interaction
   • SAM, PFIH, and VRTYSC binding assignments not biochemically tested for PPFIA2 itself
   • No localization or functional readout
2. 2019 High

   Resolved how liprin-α physically engages GIT1 and showed this interaction is functionally required for focal adhesion assembly, providing the only direct mechanistic anchor for PPFIA2 partner binding.

   Evidence Crystal structures of GIT1–liprin-α and GIT1–paxillin complexes with structure-guided GIT1 mutagenesis and focal adhesion assays in COS7 cells

   PMID:30737283

   Open questions at the time

   • Interaction characterized from the GIT1 side; PPFIA2-specific contributions versus other liprin-α paralogs not isolated
   • Focal adhesion role demonstrated via GIT1 variants, not direct PPFIA2 perturbation
   • Does not address synaptic function
3. 2025 Low

   Linked PPFIA2 to human disease, implicating it as a constraint-intolerant gene whose disruption causes neurodevelopmental disorder.

   Evidence Exome/genome sequencing of affected individuals with gnomAD constraint analysis and cohort aggregation of de novo variants

   PMID:41044885

   Open questions at the time

   • No direct cellular or in vitro mechanistic experiment on PPFIA2 function
   • Causal mechanism connecting variants to synapse phenotype untested
   • No functional validation of variant impact
4. 2025 Low

   Placed PPFIA2 protein at synapses and showed its level is responsive to the SNARE release machinery, consistent with a synaptic role.

   Evidence Quantitative mass-spectrometry proteomics of hiPSC-derived forebrain glutamatergic neurons carrying the SNAP25 I67N variant

   PMID:40181518

   Open questions at the time

   • Single proteomic dataset; PPFIA2 change is a secondary, indirect observation
   • Does not establish whether PPFIA2 acts upstream or downstream of the release machinery
   • No demonstration of PPFIA2 scaffolding activity at the synapse

• Whether PPFIA2's predicted SAM, PFIH, and VRTYSC interactions occur in cells and how its scaffolding drives synapse assembly and maturation remains undetermined.
• No experimental validation of PPFIA2 binding to LAR-PTPs, Liprin-β, KIF1A, or GRIP
• No direct cellular assay of PPFIA2 in synapse assembly
• Mechanism linking de novo variants to neuronal phenotype unknown