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Plasmodium falciparum Apn1 homolog is a mitochondrial base excision repair protein with restricted enzymatic functions
Author(s) -
Tiwari Anupama,
Kuldeep Jitendra,
Siddiqi Mohammad Imran,
Habib Saman
Publication year - 2020
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.15032
Subject(s) - ap endonuclease , base excision repair , biology , ap site , dna repair , endonuclease , exonuclease , microbiology and biotechnology , dna glycosylase , mitochondrial dna , biochemistry , dna , polymerase , gene
The malaria parasite carries two organelles, the apicoplast and mitochondrion, whose DNA genomes must be maintained for optimal function and parasite survival under genotoxic stress. DNA repair mechanism(s) operative within these organelles were explored by mining the Plasmodium falciparum nuclear genome for sequences encoding proteins of major DNA repair pathways with predicted targeting to either organelle. Of the panel of enzymes identified for base excision repair (BER), we characterized the apurinic/apyrimidinic (AP) endonuclease Pf Apn1—an EndoIV whose homolog is not known in humans. Pf Apn1 targeted to the mitochondrion and functioned as an AP endonuclease requiring both Zn 2+ and Mn 2+ ions for maximal activity. Mutation of the critical third metal‐binding site residue H542 resulted in the loss of Mn 2+ (but not Zn 2+ ) binding indicating that Mn 2+ bound Pf Apn1 at this site; this was further supported by molecular dynamic simulation. CD spectra analysis further showed requirement of both metal ions for the attainment of Pf Apn1 β‐strand‐rich optimal conformation. Pf Apn1 also functioned as a 3′‐phosphatase that would enable removal of 3′‐blocks for DNA polymerase activity during BER. Interestingly, unlike Escherichia coli and yeast EndoIV homologs, Pf Apn1 lacked 3′–5′ exonuclease activity and also did not cleave damaged bases by nucleotide incision repair (NIR). Uncoupling of endonuclease/phosphatase and exonuclease/NIR in Pf Apn1 suggests that amino acid residues distinct from those critical for endonuclease function are required for exonuclease activity and NIR. Characterization of a critical mitochondrion‐targeted AP endonuclease provides evidence for a functional BER pathway in the parasite organelle.