The HflB protease of Escherichia coli degrades its inhibitor λcIII

The cIII protein of bacteriophage λ is known to protect two regulatory proteins from degradation by the essential Escherichia coli protease HflB (also known as FtsH), viz. the λcII protein and the host heat shock sigma factor σ32, λcIII, itself an unstable protein, is partially stabilized when the HflB concentration is decreased, and its half-life is decreased when HflB is overproduced, strongly suggesting that it is degraded by HflB in vivo. The in vivo degradation of λcIII (unlike that of σ32) does not require the molecular chaperone DnaK. Furthermore, the half-life of λcIII is not affected by depletion of the endogenous ATP pool, suggesting that λcIII degradation is ATP independent (unlike that of λcII and σ32). The λcIII protein, which is predicted to contain a 22-amino-acid amphipathic helix, is associated with the membrane, and nonlethal overproduction of λcIII makes cells hypersensitive to the detergent sodium dodecyl sulfate. This could reflect a direct λcIII-membrane interaction or an indirect association via the membrane-bound HflB protein, which is known to be involved in the assembly of certain periplasmic and outer membrane proteins.SCOPUS: ar.j