ptpC (PTP3) notes — Dictyostelium discoideum, UniProt P54637

Deep research status

just deep-research-falcon DICDI ptpC --fallback perplexity-lite was run on 2026-10-05 and
FAILED: falcon returned HTTP 402 Payment Required, and the perplexity-lite fallback
reported "Provider 'perplexity' not available. Available: openai, falcon, openscientist".
No deep-research file was produced; this review is based on the cached publications below
and PubMed searches ("PTP3 Dictyostelium" returned 9 PMIDs, all now cached).

990 aa non-receptor PTP; single PTP catalytic domain (aa 422-715; PF00102, PS00383 active-site
signature), flanked by long disordered N- and C-terminal regions (UniProt). PANTHER
PTHR19134:SF549.
Two genomic copies in JH10/Ax3 background; one could be disrupted (slow growth), the other was
refractory, suggesting essentiality [PMID:8628311 "There are two copies of the PTP3 gene in this
haploid organism"; "We were unable to obtain a strain with disruptions in both PTP3 genes"].

Recombinant PTP3 has vanadate-sensitive phosphatase activity PMID:8628311. Intrinsic activity of the
bacterial enzyme is low and the PTP3 sequence is divergent at otherwise conserved residues
PMID:18305004.
C-to-S substrate-trapping mutant forms a stable complex with tyrosine-phosphorylated p130 (pp130)
PMID:10207040.
pp130 was later identified as STATc PMID:18305004. PTP3 directly interacts with and dephosphorylates STATc
PMID:18305004, removing
phosphate from Tyr922 PMID:24587195.

PTP3 overexpression makes STATc refractory to activation; a dominant inhibitor (substrate trap)
causes constitutive Tyr phosphorylation and ectopic nuclear localisation of STATc PMID:18305004.
DIF-1 and hyperosmotic stress inhibit PTP3 (transient 20% vs stable 40% activity decrease) and
induce Ser/Thr phosphorylation of PTP3, an atypical STAT-activation mechanism where the phosphatase
arm is regulated PMID:18305004.
Phosphosites S448 and S747; Ca2+-elevating agents stimulate their phosphorylation and activate
STATc PMID:20159963.
Actin cytoskeleton disruption (latrunculin A, cytochalasin A) and DIF-1 increase S747
phosphorylation PMID:22365144.
The TKL kinase Phg2 binds PTP3 in vitro and is required for full S747 phosphorylation
PMID:24587195.
CblA (Cbl homologue) positively regulates STATc by downregulating PTP3 PMID:18840649.
Pyk2 (the STATc Tyr922 kinase) co-IPs with PTP3 and they co-localize in stress-induced granules
PMID:25143406. STATc kinase is constitutive; the PTP3 phosphatase arm is the regulated arm for
DIF-1 PMID:22699506.
ptpC expression is induced by sorbitol in a STATc- and cGMP-dependent manner (positive feedback)
PMID:24587195.

Cytosolic in unstimulated cells; upon stress, translocates to structures that co-localize with
endosomal vesicles, independently of its activity PMID:10207040. Stress granules shared with
Pyk2 PMID:25143406.
Expression enriched in anterior-like and prestalk cells (lacZ reporter) PMID:8628311.

PTP activity (IDA x2, IEA): accept; core.
protein binding IPI with STATc (Q54BD4): MODIFY to STAT family protein binding (GO:0097677).
The PMID:12220630 IPI (OSBPa paper) is abstract-only; the abstract does not mention PTP3/STATc,
but per project rules I do not remove a curator IPI; the STATc interaction itself is
independently established by PMID:18305004.
protein binding IPI with Phg2 (Q54QQ1): MODIFY to protein kinase binding (GO:0019901).
protein localization to nucleus (IMP): direction is wrong — PTP3 opposes STATc nuclear
accumulation; MODIFY to negative regulation of protein localization to nucleus (GO:1900181).
Proposed NEW: peptidyl-tyrosine dephosphorylation (GO:0035335) — PTP3 itself performs the
dephosphorylation step on STATc Tyr922.