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J. Bacteriol., 04 1997, 2210-2220, Vol 179, No. 7
M Bendjennat, A Blanchard, M Loutfi, L Montagnier and E Bahraoui
The major nuclease from Mycoplasma penetrans has been purified to
homogeneity. The enzyme seems to be present as a membrane-associated
precursor of 50 kDa and as a peripheral membrane monomeric polypeptide of
40 kDa that is easily removed by washing of cells with isotonic buffers and
in the aqueous phase upon Triton partitioning of Triton X- 114-solubilized
protein. The 40-kDa nuclease was extracted from M. penetrans cells by
Triton X-114 and phase fractionation and was further purified by
chromatography on Superdex 75 and chelating Sepharose (Zn2+ form) columns.
By gel filtration, the apparent molecular mass was 40 kDa. The purified
enzyme exhibits both a nicking activity on superhelical and linear
double-stranded DNA and a nuclease activity on RNA and single-stranded DNA.
No exonuclease activity was found for this enzyme. This nuclease required
both Mg2+ (optimum, 5 mM) and Ca2+ (optimum, 2 mM) for activity and
exhibited a pH optimum between pH 7 and 8 for DNase activity. It was
inhibited by Zn2+, Mn2+, heparin, sodium dodecyl sulfate, and chelator
agents such EDTA and EGTA, but no effect was observed with ATP,
2-mercaptoethanol, N-ethylmaleimide, dithiothreitol, nonionic detergents,
phenylmethylsulfonyl fluoride, and iodoacetamide. Nuclease activity was
inhibited by diethylpyrocarbonate at both pH 6 and 8 and by pepstatin,
suggesting the involvement of a histidine and an aspartate in the active
site. When added to human lymphoblast nuclei, the purified M. penetrans
endonuclease induced internucleosomal fragmentation of the chomatin into
oligonucleosomal fragments. On the basis of this result, and taking into
account the fact that M. penetrans has the capacity to invade eucaryotic
cells, one can suggest, but not assert, that produced Ca2+/Mg2+-dependent
endonuclease may alter the nucleic acid metabolism of host cells by DNA
and/or RNA degradation and may act as a potential pathogenic determinant.
Copyright © 1997, American Society for Microbiology
Purification and characterization of Mycoplasma penetrans Ca2+/Mg2+- dependent endonuclease
Laboratory of Immunovirology UFR SVT, University of Paul Sabatier, Toulouse, France.
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