TAILIEUCHUNG - Báo cáo khoa học: The pivotal regulator GlnB of Escherichia coli is engaged in subtle and context-dependent control

This study tests the purported signal amplification capability of the gluta-mine synthetase (GS) regulatory cascade inEscherichia coli. Intracellular concentrations of the pivotal regulatory protein GlnB were modulated by varying expression of its gene (glnB). Neither glnBexpression nor PII * (. the sum of the concentration of the P II-like proteins GlnB and GlnK) had control over the steady-state adenylylation level of GS when cells were grown in the presence of ammonia | The pivotal regulator GlnB of Escherichia coli is engaged in subtle and context-dependent control Wally C. van Heeswijk1 Douwe Molenaar1 Sjouke Hoving1 and Hans V. Westerhoff1 2 1 Department of Molecular CellPhysiology Faculty of Earth and Life Sciences Vrije Universiteit Amsterdam The Netherlands 2 Manchester Centre for Integrative Systems Biology University of Manchester UK Keywords glutamine synthetase metabolic control analysis P . signal transduction cascades ultrasensitivity Correspondence W. C. van Heeswijk Faculty of Earth and Life Sciences Department of Molecular Cell Physiology Vrije Universiteit De Boelelaan 1085 NL-1081 HV Amsterdam The Netherlands Fax 31 20 598 7229 Tel 31 20 598 7228 E-mail wc_van_heeswijk@ Website http vakgroepen mcp main Present address Novartis Institutes of Biomedical Research Basel Switzerland Received 5 February 2009 revised 3 April 2009 accepted 8 April 2009 doi This study tests the purported signal amplification capability of the glutamine synthetase GS regulatory cascade in Escherichia coli. Intracellular concentrations of the pivotal regulatory protein GlnB were modulated by varying expression of its gene glnB . Neither glnB expression nor Pjj . the sum of the concentration of the PII-like proteins GlnB and GlnK had control over the steady-state adenylylation level of GS when cells were grown in the presence of ammonia in which glnK is not activated. Following the removal of ammonia the response coefficient of the transient deadenylylation rate of GS-AMP was again zero with respect to both glnB expression and Pjj concentration. This was at wild-type Pjj levels. A 20 decrease in the Ph level resulted in the response coefficients increasing to 1 which was quite significant yet far from expected for zero-order ultrasensitivity. The transient deadenylylation rate of GS-AMP after brief incubation with ammonia was also measured in cells grown in the absence of

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