Disease mutations in the human mitochondrial DNA polymerase thumb subdomain impart severe defects in mitochondrial DNA replication.

Abstract

Forty-five different point mutations in POLG, the gene encoding the catalytic subunit of the human mitochondrial DNA polymerase (pol gamma), cause the early onset mitochondrial DNA depletion disorder, Alpers syndrome. Sequence analysis of the C-terminal polymerase region of pol gamma revealed a cluster of four Alpers mutations at highly conserved residues in the thumb subdomain (G848S, c.2542g-->a; T851A, c.2551a-->g; R852C, c.2554c-->t; R853Q, c.2558g-->a) and two Alpers mutations at less conserved positions in the adjacent palm subdomain (Q879H, c.2637g-->t and T885S, c.2653a-->t). Biochemical characterization of purified, recombinant forms of pol gamma revealed that Alpers mutations in the thumb subdomain reduced polymerase activity more than 99% relative to the wild-type enzyme, whereas the palm subdomain mutations retained 50-70% wild-type polymerase activity. All six mutant enzymes retained physical and functional interaction with the pol gamma accessory subunit (p55), and none of the six mutants exhibited defects in misinsertion fidelity in vitro. However, differential DNA binding by these mutants suggests a possible orientation of the DNA with respect to the polymerase during catalysis. To our knowledge this study represents the first structure-function analysis of the thumb subdomain in pol gamma and examines the consequences of mitochondrial disease mutations in this region.

• Authors: Rajesh Kasiviswanathan, Matthew J Longley, Sherine S L Chan, William C Copeland
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 284 Issue 29 Pg. 19501-10 (Jul 17 2009) ISSN: 0021-9258 [Print] United States
• PMID: 19478085 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, N.I.H., Intramural)

Chemical References

• DNA, Mitochondrial
• Oligonucleotides
• Protein Subunits
• Recombinant Proteins
• DNA Polymerase gamma
• DNA-Directed DNA Polymerase

Topics

• Amino Acid Sequence
• Animals
• Binding Sites (genetics)
• Catalysis
• Cell Line
• Circular Dichroism
• DNA Polymerase gamma
• DNA Replication (genetics)
• DNA, Mitochondrial (genetics)
• DNA-Directed DNA Polymerase (chemistry, genetics, metabolism)
• Diffuse Cerebral Sclerosis of Schilder (genetics)
• Humans
• Immunoblotting
• Kinetics
• Molecular Sequence Data
• Mutation
• Oligonucleotides (genetics, metabolism)
• Protein Binding
• Protein Subunits (genetics, metabolism)
• Recombinant Proteins (chemistry, metabolism)
• Sequence Homology, Amino Acid
• Spodoptera