InterPro CAP/SCP signatures map PR1B1 to the extracellular region, consistent with its cleaved signal peptide and apoplastic localization.

SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.

For PR1B1 the SPKW pipeline produced "killing of cells of another organism" and "defense response to fungus" from the Antimicrobial, Fungicide and Plant defense keywords; these capture real biology but at an over-strong or slightly imprecise level of specificity.

The ARBA model assigns the broad term "defense response to other organism", an accurate and appropriate replacement for the retired SPKW defense annotations.

The P6/P14 protein (PR1B1) is one of the extracellular PR proteins of tomato; cDNA clones for the extracellular P14 isomers P4 and P6 were isolated.

PR protein mRNAs accumulate upon infection by the fungal pathogen Cladosporium fulvum.

PR1b1 is not constitutively expressed but is transcriptionally activated following pathogen attack, locally in tissues undergoing the hypersensitive response.

PR1b1 expression is induced by both salicylic acid and ethylene precursors.

The original protein sequencing of tomato leaf protein p14 (= PR1B1) defined a new structural protein type, the founding sequence of the CAP superfamily.

The NMR structure of P14a (= PR1B1; PDB 1CFE) revealed a novel alpha-beta-alpha sandwich CAP fold.

P14a displays antifungicidal activity and is induced in tomato leaves in response to pathogen infection.

Tomato P14a, P14b and P14c proteins directly inhibit Phytophthora infestans zoospore germination in vitro and reduce infected leaf surface in vivo.

PR-1 proteins display differential fungicidal activity; tomato P14a (= PR1B1) was the weakest and tomato P14c the most efficient.

PR-1 / CAP-superfamily proteins bind sterols; their antimicrobial action is caused by sequestration of sterol away from pathogens.

Sterol-auxotroph pathogens such as the oomycete Phytophthora are particularly sensitive to PR-1.

The CAPE1 immune-signalling peptide is derived from the C-terminus of tomato PR-1b (PR1B1).

CAPE1 is a wound/MeJA-induced DAMP elicitor that activates SA/JA-dependent anti-pathogen defense gene expression, highlighting a role for PR-1 in immune signalling.

PR1 is the founding member of the CAP superfamily; its precise mode of action has remained elusive, with sterol/lipid binding by the CAP domain the leading mechanism.

Plant PR1 is proteolytically cleaved to release the C-terminal CAPE1 peptide, which is sufficient to activate an immune response; PR1 overexpression increases pathogen resistance.

PR1B1 (P04284) is explicitly recognized in the CAP protein literature as a bona fide CAP-family representative, and tomato PR1b1 was cloned as accession Y08804 (the basic, pathogen-responsive PR-1 isoform), confirming the target gene identity.

Tomato PR-1 family proteins act as direct extracellular antimicrobial / anti-oomycete defense proteins - basic PR-1 proteins inhibit Phytophthora infestans zoospore germination in vitro and reduce lesion area in vivo, with basic isoforms more antifungal than acidic counterparts; this is family-level evidence and the report notes no PR1B1-specific cytotoxic "killing" assay exists.

PR1 proteins are proteolytically processed in the apoplast to release the 11-amino-acid C-terminal peptide CAPE1, which induces ROS and defense gene expression and confers resistance to Pseudomonas syringae without a hypersensitive response; processing is blocked by serine-protease inhibitors in apoplastic fluid.

PR1B1 is a secretory-pathway precursor with a 24-aa N-terminal signal peptide; closely linked tomato PR-1 protein P1(P14) localizes to both the apoplast (intercellular spaces) and vacuolar inclusion bodies, supporting an extracellular site of action.

A precise sterol-binding affinity for tomato PR1B1 specifically is NOT present in the retrieved literature; lipid/sterol binding is discussed at the CAP-superfamily level via hydrophobic ligand-binding pockets, consistent with the ISS evidence code used for the sterol-binding annotation.