OpenAntigens: antigen construct-design reports for human and mouse cell-surface and secreted proteins (snapshot 2026-06-11)

Choosing which region of a protein to express is one of the least standardized steps in antibody discovery, recombinant reagent generation, structural biology and computational binder design. For human cell-surface and secreted proteins it means reconciling topology, processing, predicted and experimental structure, modifications, interaction partners, orthologs, paralogs and cross-reactivity risk before any DNA is ordered, target by target. OpenAntigens is a freely available, no-login database that organizes this target-side evidence into per-target, construct-ready reports. For 5,328 human secreted, GPI-anchored, single-pass and multipass proteins, it integrates UniProt topology, AlphaFold pLDDT and PAE, PDB precedent, InterPro and Pfam domains, mouse and cynomolgus orthologs, paralog and family context, Open Targets disease associations, and local BLAST cross-reactivity screens, and uses AlphaFold confidence to propose construct candidates, yielding 56,148 candidates and 148,721 cross-reactivity hits across the release. An interactive construct designer links the sequence, AlphaFold structure, pLDDT and PAE so users can adjust boundaries in the browser and export species-equivalent sequences with real-time cysteine and modification warnings. Unlike surfaceome, secretome or single-protein domain-boundary resources, OpenAntigens is the only one to pair a defined surface and secreted target universe with structure-aware boundary logic, species-equivalent regions, specificity context and in-browser export for the construct-selection task. It supports both classical antibody workflows and the growing need to prepare target constructs for AI-designed binders. OpenAntigens is available at openantigens.org. This record is the data layer of the 2026-06-11 build: one structured report (*_report.json) and one readable report (*_report.md) per target — 5,326 human and 4,700 mouse targets — plus master indexes, ortholog/paralog reference tables, family alignments, and the Open Targets disease-association table. The rendered website, raw AlphaFold structures, BLAST databases, and regenerable figures are excluded; browse the full interactive portal at https://openantigens.org. See snapshot_manifest.json for exact provenance and DATA_LICENSE.md for source-data terms.