PSTK

Gene Description

PSTK is O-phosphoseryl-tRNA(Sec) kinase (also called L-seryl-tRNA(Sec) kinase or phosphoseryl-tRNA[Ser]Sec kinase; EC 2.7.1.164), an ATP-dependent tRNA kinase that acts in the biosynthesis of selenocysteine on its tRNA. It specifically phosphorylates the seryl moiety of L-seryl-tRNA(Sec), using ATP and Mg(2+), to produce O-phosphoseryl-tRNA(Sec) plus ADP. This O-phosphoseryl-tRNA(Sec) is the activated intermediate that the enzyme SEPSECS subsequently converts, using selenophosphate, to selenocysteyl-tRNA(Sec), the charged tRNA that decodes in-frame UGA codons as selenocysteine during translation of selenoproteins. PSTK is highly substrate-specific, acting on tRNA(Sec) and not on other tRNAs, and belongs to the KTI12/PSTK-related family with a P-loop nucleotide-binding fold. The enzyme is conserved across eukaryotes and archaea that possess the selenocysteine incorporation machinery, and is dispensable in organisms that lack selenoproteins.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0000049 tRNA binding	IBA GO_REF:0000033	ACCEPT	Summary: tRNA binding is a well-supported molecular function for PSTK: its catalytic substrate is L-seryl-tRNA(Sec), so it must recognize and bind tRNA(Sec). This IBA call is consistent with the enzymatic role and is retained as a supporting (non-core, but accepted) molecular function that underlies the core kinase activity. Reason: PSTK acts on a tRNA substrate; UniProt states it phosphorylates seryl-tRNA(Sec), which requires tRNA binding. The phylogenetic (IBA) inference is biologically sound. Supporting Evidence: file:human/PSTK/PSTK-uniprot.txt Specifically phosphorylates seryl-tRNA(Sec) to O-
GO:0016301 kinase activity	IBA GO_REF:0000033	MODIFY	Summary: Kinase activity is correct but far more general than what is known for PSTK. The specific molecular function is L-seryl-tRNA(Sec) kinase activity (GO:0043915), which is a direct child of kinase activity (GO:0016301). The annotation should be refined to the specific term. Reason: GO:0016301 is an over-general parent; the specific catalytic activity (ATP-dependent phosphorylation of the seryl moiety of L-seryl-tRNA(Sec)) is captured by GO:0043915, which is already annotated. Replace with the specific child term. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Proposed replacements: L-seryl-tRNA(Sec) kinase activity Supporting Evidence: file:human/PSTK/PSTK-uniprot.txt Reaction=L-seryl-tRNA(Sec) + ATP = O-phospho-L-seryl-tRNA(Sec) + ADP;
GO:0043915 L-seryl-tRNA(Sec) kinase activity	IEA GO_REF:0000120	ACCEPT	Summary: This is the correct, specific core molecular function of PSTK. The IEA is derived from the RHEA reaction (RHEA:25037) and EC number 2.7.1.164, both of which match the UniProt catalytic activity exactly (ATP + L-seryl-tRNA(Sec) = ADP + O-phospho-L-seryl-tRNA(Sec)). Reason: The EC/RHEA-derived term is the precise enzymatic activity of PSTK and matches the curated UniProt reaction and family assignment. Supporting Evidence: file:human/PSTK/PSTK-uniprot.txt Reaction=L-seryl-tRNA(Sec) + ATP = O-phospho-L-seryl-tRNA(Sec) + ADP; file:human/PSTK/PSTK-uniprot.txt Belongs to the L-seryl-tRNA(Sec) kinase family.
GO:0043915 L-seryl-tRNA(Sec) kinase activity	ISS GO_REF:0000024	ACCEPT	Summary: Same specific core molecular function as the IEA annotation, here inferred by sequence similarity (ISS) from the experimentally characterized mouse ortholog (UniProtKB:Q8BP74). This is a valid, converging line of evidence for the L-seryl-tRNA(Sec) kinase activity. Reason: ISS transfer from the mouse ortholog Q8BP74 (the reference UniProt entry for the catalytic activity) supports the same specific enzymatic function; consistent with the IEA/EC and IBA evidence. Duplicate of the IEA term but from an independent method. Supporting Evidence: file:human/PSTK/PSTK-uniprot.txt phosphoseryl-tRNA(Sec), an activated intermediate for selenocysteine
GO:0001717 conversion of seryl-tRNAsec to selenocys-tRNAsec	IEA GO_REF:0000120	NEW	Summary: Proposed biological-process annotation, not present in the seeded GOA set. PSTK catalyzes the phosphorylation step (Ser-tRNA(Sec) -> O-phosphoseryl-tRNA(Sec)) that is part of the tRNA-based conversion of serine to selenocysteine; this BP directly reflects the pathway role captured by UniProt (aminoacyl-tRNA biosynthesis; selenocysteinyl-tRNA(Sec) biosynthesis). This is the precise, non-obsolete BP term for the process. Reason: Adds the specific biological process for PSTK's pathway role, consistent with the curated UniProt PATHWAY line and complementing the molecular-function annotations. Supporting Evidence: file:human/PSTK/PSTK-uniprot.txt selenocysteinyl-tRNA(Sec) from L-seryl-tRNA(Sec) file:human/PSTK/PSTK-uniprot.txt phosphoseryl-tRNA(Sec), an activated intermediate for selenocysteine

Core Functions

O-phosphoseryl-tRNA(Sec) (L-seryl-tRNA(Sec)) kinase: ATP- and Mg(2+)-dependent phosphorylation of the seryl moiety of L-seryl-tRNA(Sec) to O-phosphoseryl-tRNA(Sec), the activated intermediate of the selenocysteine tRNA-charging pathway. PSTK binds tRNA(Sec) and ATP to carry out this reaction.

Molecular Function:

L-seryl-tRNA(Sec) kinase activity

Directly Involved In:

conversion of seryl-tRNAsec to selenocys-tRNAsec

Substrates:

Ser-tRNA(Sec) polyanion

Supporting Evidence:

file:human/PSTK/PSTK-uniprot.txt
Reaction=L-seryl-tRNA(Sec) + ATP = O-phospho-L-seryl-tRNA(Sec) + ADP;
file:human/PSTK/PSTK-uniprot.txt
phosphoseryl-tRNA(Sec), an activated intermediate for selenocysteine
file:human/PSTK/PSTK-uniprot.txt
selenocysteinyl-tRNA(Sec) from L-seryl-tRNA(Sec)

Gene Description

Existing Annotations Review

Core Functions

O-phosphoseryl-tRNA(Sec) (L-seryl-tRNA(Sec)) kinase: ATP- and Mg(2+)-dependent phosphorylation of the seryl moiety of L-seryl-tRNA(Sec) to O-phosphoseryl-tRNA(Sec), the activated intermediate of the selenocysteine tRNA-charging pathway. PSTK binds tRNA(Sec) and ATP to carry out this reaction.

References

📚 Additional Documentation

Notes

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