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Acta Biochimica et Biophysica Sinica Advance Access originally published online on July 17, 2009
Acta Biochimica et Biophysica Sinica 2009 41(8):709-717; doi:10.1093/abbs/gmp059
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© The Author 2009. Published by ABBS Editorial Office in association with Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences.

Evidences of Hfq associates with tryptophanase and affects extracellular indole levels

Yinghua Zhang1,2 and Guofan Hong1,*

1 State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
2 Graduate School of the Chinese Academy of Sciences, Shanghai 200031, China

* Correspondence address. Tel: +86-21-54921223; Fax: +86-21-54921011; E-mail: gfhong{at}sibs.ac.cn


  Abstract

In this study, we observed a novel property of Escherichia coli Hfq protein: it possibly influenced extracellular indole levels. The extracellular indole concentrations were increased in Hfq mutant cells and decreased in Hfq overexpression cells in a cell density-dependent manner. The decreased extracellular indole levels in Hfq overexpression cells caused the postponement of entering into stationary phase. Indole was produced by tryptophanase, the gene product of tnaA, which catalyzed tryptophan into indole, ammonia and pyruvate. Further studies showed that at cell density of 0.8 but not at 0.4, tryptophanase activities of total cell extracts were affected by Hfq mutation or overexpression. Protein pull-down assay and co-immunoprecipitation experiments revealed that Hfq associated with tryptophanase under relatively higher extracellular indole levels, suggesting this was a feedback control of indole production. The association of Hfq and tryptophanase might be indirect because purified Hfq could not affect the values of Km and Vmax of purified tryptophanase.

Keywords    Hfq; tryptophanase; indole

Received: March 3, 2009; Accepted: April 13, 2009
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