N. Vasquez-laslop et al., Molecular sieve mechanism of selective release of cytoplasmic proteins by osmotically shocked Escherichia coli, J BACT, 183(8), 2001, pp. 2399-2404
Escherichia coli cells, the outer membrane of which is permeabilized with E
DTA, release a specific subset of cytoplasmic proteins upon a sudden drop i
n osmolarity in the surrounding medium. This subset includes EF-Tu, thiored
oxin, and DnaK among other proteins, and comprises similar to 10% of the to
tal bacterial protein content. As we demonstrate here, the same proteins ar
e released from electroporated E. coli cells pretreated with EDTA, Although
known for several decades, the phenomenon of selective release of proteins
has received no satisfactory explanation. Here we show that the subset of
released proteins is almost identical to the subset of proteins that are ab
le to pass through a 100-kDa-cutoff cellulose membrane upon molecular filtr
ation of an E. coli homogenate. This finding indicates that in osmotically
shocked or electroporated bacteria, proteins are strained through a molecul
ar sieve formed by the transiently damaged bacterial envelope. As a result,
proteins of small native sizes are selectively released, whereas large pro
teins and large protein complexes are retained by bacterial cells.