Biochemical studies with DNA polymerase beta and DNA polymerase beta-PAK of Trypanosoma cruzi suggest the involvement of these proteins in mitochondrial DNA maintenance.
Mammalian DNA polymerase beta is a nuclear enzyme involved in the base excision and single-stranded DNA break repair pathways. In trypanosomatids, this protein does not have a defined cellular localization, and its function is poorly understood. We characterized two Trypanosoma cruzi proteins homologous to mammalian DNA polymerasebeta, TcPolbeta and TcPolbetaPAK, and showed that both enzymes localize to the parasite kinetoplast. In vitro assays with purified proteins showed that they have DNA polymerization and deoxyribose phosphate lyase activities. Optimal conditions for polymerization were different for each protein with respect to dNTP concentration and temperature, and TcPolbetaPAK, in comparison to TcPolbeta, conducted DNA synthesis over a much broader pH range. TcPolbeta was unable to carry out mismatch extension or DNA synthesis across 8-oxodG lesions, and was able to discriminate between dNTP and ddNTP. These specific abilities of TcPolbeta were not observed for TcPolbetaPAK or other X family members, and are not due to a phenylalanine residue at position 395 in the C-terminal region of TcPolbeta, as assessed by a site-directed mutagenesis experiment reversing this residue to a well conserved tyrosine. Our data suggest that both polymerases from T. cruzi could cooperate to maintain mitochondrial DNA integrity through their multiple roles in base excision repair, gap filling and translesion synthesis.
Lopes
Débora de Oliveira
Dde O
Departamento de Bioquímica e Imunologia, ICB/UFMG, Brazil.
Schamber-Reis
Bruno Luiz Fonseca
BL
Regis-da-Silva
Carlos Gustavo
CG
Rajão
Matheus Andrade
MA
Darocha
Wanderson Duarte
WD
Macedo
Andréa Mara
AM
Franco
Glória Regina
GR
Nardelli
Sheila Cristina
SC
Schenkman
Sérgio
S
Hoffmann
Jean-Sébastien
JS
Cazaux
Christophe
C
Pena
Sérgio Danilo Junho
SD
Teixeira
Santuza Maria Ribeiro
SM
Machado
Carlos Renato
CR