Gene Ontology annotation through association of InterPro records with GO terms

PITP family domain (IPR001666) associated with phospholipid transport

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

Annotations transferred from human PITPNC1 (Q9UKF7)

GO_REF:0000033

Annotation inferences using phylogenetic trees

Phylogenetic inference of PITP family conserved functions

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

Machine learning predictions for phospholipid binding, cytoplasm, and nucleus localization

PMID:10531358

Cloning and characterization of a novel human phosphatidylinositol transfer protein, rdgBbeta.

Human rdgBbeta (PITPNC1) cloned and characterized as a novel PITP lacking transmembrane domains

"In contrast to other rdgB-like proteins, MrdgBbeta contains no transmembrane motifs or the conserved carboxyl-terminal domain"
Cytoplasmic localization demonstrated by immunofluorescence

"Immunofluorescence analysis of ectopic MrdgBbeta showed cytoplasmic staining"
PI transfer activity demonstrated in vitro

"the ability of recombinant MrdgBbeta to transfer phosphatidylinositol in vitro was similar to other PITP-like domains"
Ubiquitous expression with highest levels in heart, muscle, kidney, liver, and leukocytes

"MrdgBbeta mRNA is ubiquitously expressed"

PMID:22822086

Phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) binds and transfers phosphatidic acid.

PITPNC1/RdgBbeta binds and transfers both PI and phosphatidic acid (PA)

"besides PI, RdgBβ binds and transfers phosphatidic acid (PA) but hardly binds phosphatidylcholine"
Does not significantly bind phosphatidylcholine, unlike Class I PITPs

"the lipid binding properties of this protein are distinct to Class I PITPs because, besides PI, RdgBβ binds and transfers phosphatidic acid (PA) but hardly binds phosphatidylcholine"
Purified RdgBbeta preloaded with PA and phosphatidylglycerol from E. coli

"RdgBβ when purified from Escherichia coli is preloaded with PA and phosphatidylglycerol"
PA binding increases at the expense of PI binding when phospholipase D is activated

"After an increase in PA levels following activation of endogenous phospholipase D...binding of PA to RdgBβ was greater at the expense of PI binding"

PMID:21728994

The phosphatidylinositol transfer protein RdgBβ binds 14-3-3 via its unstructured C-terminus, whereas its lipid-binding domain interacts with the integral membrane protein ATRAP (angiotensin II type I receptor-associated protein).

RdgBbeta C-terminus binds 14-3-3 at two phosphorylated sites

"the C-terminus contains two tandem phosphorylated binding sites (Ser(274) and Ser(299)) for 14-3-3"
14-3-3 binding shields PEST sequences and stabilizes the protein

"The C-terminus also contains PEST sequences which are shielded by 14-3-3 binding"
PITP domain interacts with ATRAP to recruit RdgBbeta to membranes

"the PITP domain of RdgBβ interacts with the integral membrane protein ATRAP"
RdgBbeta is degraded by proteasome with half-life of 4h; faster without 14-3-3 binding

"RdgBβ is degraded with a half-life of 4 h following ubiquitination via the proteasome"

PMID:26977884

PITPNC1 Recruits RAB1B to the Golgi Network to Drive Malignant Secretion.

PITPNC1 amplified in breast cancer and overexpressed in metastatic cancers

"PITPNC1 as a gene amplified in a large fraction of human breast cancer and overexpressed in metastatic breast, melanoma, and colon cancers"
PITPNC1 binds Golgi-resident PI4P and recruits RAB1B to the Golgi

"PITPNC1 promotes malignant secretion by binding Golgi-resident PI4P and localizing RAB1B to the Golgi"
Drives secretion of pro-invasive and pro-angiogenic factors

"PITPNC1-mediated vesicular release drives metastasis by increasing the secretion of pro-invasive and pro-angiogenic mediators HTRA1, MMP1, FAM3C, PDGFA, and ADAM10"

file:DROME/rdgBbeta/rdgBbeta-notes.md

Research notes on rdgBbeta gene review

rdgBbeta alleles (EP2360, G8057) ameliorate ALS-like phenotype in Vap33-P58S model
BioReason prediction incorrectly attributes Class I PITP functions (cytokinesis, PC binding) to this Class IIB PITP

file:DROME/rdgBbeta/rdgBbeta-deep-research-falcon.md

Falcon deep research report on rdgBbeta (Drosophila, CG17818, Q9U9P7)

rdgBbeta encodes a soluble Class IIB PITP-domain protein, the smaller PITP-domain-only member of the RdgB family, distinct from the multi-domain RdgBalpha phototransduction protein that localizes to ER-PM contact sites via VAP.

"RdgBβ is explicitly described as a **soluble class IIB PITP** that binds other proteins (e.g., 14-3-3, ATRAP) for functional recruitment to membranes—distinct from multi-domain RdgBα proteins that localize to ER–PM contact sites via VAP."
RdgBbeta is structurally and functionally distinct from RdgBalpha; the two should not be conflated. RdgBalpha is a multidomain protein with FFAT/DDHD modules at ER-PM contact sites, whereas rdgBbeta is a small soluble PITP recruited to membranes by protein partners.

"RdgBβ is a **small soluble** PITP with a short disordered tail and protein-partner-mediated membrane recruitment, whereas **RdgBα** is a **multidomain** protein with FFAT/DDHD/LSN2-related modules that localizes to **ER–PM contact sites** via VAP."
The RdgBbeta subfamily preferentially binds and transfers PI and PA with very little PC, and can transfer PA robustly, distinguishing it from Class I PITPs that exchange PI and PC.

"Expert review synthesis proposes that RdgBβ-class proteins preferentially bind/transfer **phosphatidylinositol (PI)** and **phosphatidic acid (PA)** with **very little phosphatidylcholine (PC)**, and that RdgBβ can transfer **PA robustly**, a property not typical of class I PITPs."
In vitro PI-transfer activity of the mammalian ortholog RdgBbeta/PITPNC1 is very weak relative to canonical PITPalpha, supporting a model where function depends on context-specific membrane recruitment rather than bulk cytosolic transfer.

"Direct quantitative assays in a Biochemical Journal primary paper on **RdgBβ/PITPNC1** report **very weak PI-transfer activity** compared with PITPα"
RdgBbeta/PITPNC1 is mainly cytosolic at baseline and is recruited to membranes upon stimulation, consistent with the GO cytoplasm localization annotations.

"RdgBβ/PITPNC1 is described as **mainly cytosolic** at baseline and can be recruited to membranes upon specific stimuli."
The primary molecular function best supported by current evidence is PI/PA binding/transfer (not PC), coupled to phosphoinositide signaling, acting locally at membranes upon recruitment; direct Drosophila CG17818-specific mechanistic evidence remains limited.

"Its **primary molecular function** is most plausibly **binding/transfer of PI and PA (not PC)** and participation in lipid homeostasis coupled to phosphoinositide signaling, likely acting **locally at membranes upon recruitment** (family-level inference)"
Caveat: the Drosophila rdgBbeta isoform lacks the short C-terminal extension present in human RdgBbeta, so mammalian C-terminal regulatory findings (e.g., Ser274/Ser299 14-3-3 docking) should be transferred to Drosophila CG17818/Q9U9P7 only after verifying conservation.

"The Drosophila rdgBβ isoform is explicitly noted to **lack the short carboxy-terminal extension** present in human RdgBβ."