4 research outputs found
Degradation of -Glutamate Dehydrogenase from Escherichia coli: Allosteric Regulation of Enzyme Stability
Turnover of Endogenous SsrA-tagged Proteins Mediated by ATP-dependent Proteases in Escherichia coli*S⃞
Formation and degradation of SsrA-tagged proteins enable ribosome recycling
and elimination of defective products of incomplete translation. We produced
an antibody against the SsrA peptide and used it to measure the amounts of
SsrA-tagged proteins in Escherichia coli cells without interfering
with tagging or altering the context of the tag added at the ends of nascent
polypeptides. SsrA-tagged proteins were present in very small amounts unless a
component of the ClpXP protease was missing. From the levels of tagged
proteins in cells in which degradation is essentially blocked, we calculate
that ≥1 in 200 translation products receives an SsrA tag. ClpXP is
responsible for ≥90% of the degradation of SsrA-tagged proteins. The
degradation rate in wild type cells is ≥1.4 min–1 and
decreases to ∼0.10 min–1 in a clpX mutant. The
rate of degradation by ClpXP is decreased ∼3-fold in mutants lacking the
adaptor SspB, whereas degradation by ClpAP is increased 3–5-fold.
However, ClpAP degrades SsrA-tagged proteins slowly even in the absence of
SspB, possibly because of interference from ClpA-specific substrates. Lon
protease degrades SsrA-tagged proteins at a rate of ∼0.05
min–1 in the presence or absence of SspB. We conclude that
ClpXP, together with SspB, is uniquely adapted for degradation of SsrA-tagged
proteins and is responsible for the major part of their degradation in
vivo