Title |
Characterization of cell death in Escherichia coli mediated by XseA, a large subunit of exonuclease VII |
Author |
Hyeim Jung, Junwei Liang, Yuna Jung, and Dongbin Lim* |
Address |
School of Systems Biomedical Science, Soongsil University, Seoul 06978, Republic of Korea |
Bibliography |
Journal of Microbiology, 53(12),820-828, 2015,
|
DOI |
10.1007/s12275-015-5304-0
|
Key Words |
exonuclease VII, XseA, apoptosis, msDNA, ExoVII,
retron, bacterial cell death, apoptosis-like cell death |
Abstract |
Exonuclease VII (ExoVII) of Escherichia coli is a single strandspecific
DNA nuclease composed of two different subunits:
the large subunit, XseA, and the small subunit, XseB. In
this study, we found that multicopy single-stranded DNAs
(msDNAs), Ec83 and Ec78, are the in vivo substrates of
ExoVII; the enzyme cuts the phosphodiester bond between
the fourth and fifth nucleotides from the 5′ end. We used
this msDNA cleavage to assess ExoVII activity in vivo. Both
subunits were required for enzyme activity. Expression of
XseA without XseB caused cell death, even though no ExoVII
activity was detected. The lethality caused by XseA was rescued
by surplus XseB. In XseA-induced death, cells were
elongated and multinucleated, and their chromosomes were
fragmented and condensed; these are the morphological
hallmarks of apoptotic cell death in bacteria. A putative caspase
recognition sequence (FVAD) was found in XseA, and
its hypothetical caspase product with 257 amino acids was
as active as the intact protein in inducing cell death. We propose
that under ordinary conditions, XseA protects chromosome
as a component of the ExoVII enzyme, but in some
conditions, the protein causes cell death; the destruction of
cell is probably carried out by the amino terminal fragment
derived from the cleavage of XseA by caspase-like enzyme. |