PPP4R4 is a cytosolic regulatory subunit of protein phosphatase 4. It forms a stable complex with the PP4 catalytic subunit that is distinct from complexes containing PP4R1 or PP4R2–PP4R3. Its association changes PP4 activity and subcellular organization rather than providing intrinsic phosphatase catalysis.
The primary affinity-purification study identifies PP4R4 as a stable PP4c-specific partner and distinguishes it from PP2A/PP6 interactions and other PP4 regulatory complexes. PP4R4-associated activity toward fluorogenic substrate and gammaH2AX is lower than free PP4c and different from PP4R2/3-associated activity. This supports a regulatory subunit and an inhibitory effect in the tested assays, but does not establish that it inhibits all physiological PP4 substrates. It also does not establish blastocyst hatching. The selected horse sequence is nearly full-length and highly conserved, allowing stronger transfer of complex membership than a particular developmental phenotype.
From PMID:18715871(https://pubmed.ncbi.nlm.nih.gov/18715871/):
we identify a novel, stable cytosolic PP4c interacting partner, KIAA1622, which we have renamed PP4R4.
The exact target is A0A9L0S961, not an arbitrary horse record with a matching name. The reproducible paired-sequence analysis records identity, coverage and internal gaps. It supports homology but is not a reciprocal orthology test. Molecular properties are transferred only with the relevant domain, targeting and paralog constraints. The prediction-time sequence is not independently verified.
The following annotation scopes need source-specific follow-up: protein binding. Experimental annotations are not removed merely because a cached abstract omits the gene or a specific assay. High-throughput protein-binding rows require their actual partner or complex context before replacement with an informative molecular function.