This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Jewett, M. C. Articles by Swartz, J. R. PubMed PubMed Citation Articles by Jewett, M. C. Articles by Swartz, J. R.

 Previous Article  |  Next Article 

J. Bacteriol. doi:10.1128/JB.00852-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Continued protein synthesis at low [ATP] and [GTP] enables cell adaptation during energy limitation

Department of Chemical Engineering, and Department of Bioengineering, Stanford University, Stanford, California 94305 USA

^* To whom correspondence should be addressed. Email: jswartz{at}stanford.edu.

	Abstract

One of biology's critical ironies is the need to adapt to periods of energy limitation by using the energy intensive process of protein synthesis. Although previous work has identified the individual energy requiring steps for protein synthesis, we still lack an understanding of the dependence of protein biosynthesis rate on [ATP] and [GTP]. Here, we use an integrated Escherichia coli cell-free platform that mimics the intracellular, energy-limited environment to show that protein synthesis rate is governed by simple Michaelis-Menten dependencies on [ATP] and [GTP] (K_m^ATP = 27 ± 4µM, K_m^GTP = 14 ± 2µM). Although the system-level GTP affinity agrees well with the individual affinities of the GTP-dependent translation factors, the system-level K_m^ATP is unexpectedly low. Especially during starvation conditions, when energy sources are limited, cells will need to replace catalysts that become inactive and to produce new catalysts in order to effectively adapt. Our results show how this crucial survival priority for synthesizing new proteins can be enforced after rapidly growing cells encounter energy limitation. A diminished energy supply can be rationed based on the relative ATP and GTP affinities, and, since these affinities for protein synthesis are high, the cells can adapt with substantial changes in protein composition. Furthermore, our work suggests that the characterization of individual enzymes may not always predict the performance of multi-component systems with complex interdependencies. We anticipate that cell-free studies which activate complex metabolic systems will be valuable tools for elucidating the behavior of such systems.