Journal of Inorganic Biochemistry 133 (2014) 57
Contents lists available at ScienceDirect
Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio
Preface: Gas and redox sensors special issue
Cellular responses to a changing environment are crucial for tissue development, adaptation to nutrient availability, and proliferation. Although gas molecules are among the most crucial factors for transient signaling, the molecular mechanisms for the response to many of these “gasogens” remain controversial. Similarly, whereas the redox poise of the cell is clearly an important constraint on metabolism and proliferation, the mechanism for redox sensing is full of rich and varied biochemistry. Metalloenzymes play prominent roles in binding gasogens and responding to redox events wherever these pathways are known, making this mini-issue on gas and redox sensors of particular interest to the readership of JIB. Gasses and redox sensors present a number of challenges to researchers in this area. The chemical state of these analytes can make it challenging to measure solution concentrations under many experimental conditions. This largely reflects the gaseous state of ethylene, CO, NO, and O2 as well as the high vapor pressure of H2S. A further challenge arises due to the speciation of the gasogens in solution via protonation or redox equilibria, leading to closely affiliated species such as NO− and O− 2 . As a result, correlating experimental conditions with concentration data requires a great deal of care. Each gasogen is toxic in high concentration, as can be anomalous redox poise, further challenging researchers to distinguish a gas/redox sensing response from a toxicity response. While binding or reacting with a gas may lead to chemical changes in metalloproteins, sensing requires some sort of output that alters cellular function. Identifying signal transduction adds a layer of complexity to gas and redox sensing. Furthermore, sensing is not typically due to conversion of a sensor between on/off states but rather arises from changes in the relative rates of competing pathways. This leads to serious debates over the physiological significance of gas-binding affinities when these values lay outside of the physiological range. The cross-talk between various gasogens, redox poise, and other nutrients is significant, with O2 a notable central player. This is partially due to the connection between pO2 and aerobic metabolism but addi-
http://dx.doi.org/10.1016/j.jinorgbio.2014.02.008 0162-0134/© 2014 Published by Elsevier Inc.
tionally arises due to the oxidation and reduction of some of the gasogens due either to direct reaction with O2 or with various redox agents within the cell. Furthermore, iron metabolism and O2 homeostasis are closely connected, making it a real challenge to isolate one variable from the other. Redox poise is a basal reporter on cellular metabolism, leading cells to adapt to changes in redox status. This likely plays an important role in proliferation and dormancy, due in part to changes in metabolic demands. It also plays a significant role in facultative organisms that can utilize multiple terminal electron acceptors, such as for chemolithotrophic organisms. The adaptation to redox poise may significantly impact the design and utility of microbial fuel cells, in which microbes must deliver electrons to an electrode surface rather than to a diffusible oxidant. Developing chemical tools to interrogate and manipulate gasogen concentrations and redox poise is currently of much interest. Such chemical tools are pushing our abilities to directly measure cellular activity in real time and are forming the basis for medical imaging and therapeutic agents. Although far from comprehensive, articles within this issue present selected approaches to these topics. The selection of review articles in this special issue provides different perspectives on the mechanisms of gas and redox sensing as well as on the biological and technological impacts of these sensory processes.
Michael J. Knapp Guest editor Department of Chemistry, University of Massachusetts, Amherst, Amherst, MA 01003, USA
Contents lists available at ScienceDirect
Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio
Preface: Gas and redox sensors special issue
Cellular responses to a changing environment are crucial for tissue development, adaptation to nutrient availability, and proliferation. Although gas molecules are among the most crucial factors for transient signaling, the molecular mechanisms for the response to many of these “gasogens” remain controversial. Similarly, whereas the redox poise of the cell is clearly an important constraint on metabolism and proliferation, the mechanism for redox sensing is full of rich and varied biochemistry. Metalloenzymes play prominent roles in binding gasogens and responding to redox events wherever these pathways are known, making this mini-issue on gas and redox sensors of particular interest to the readership of JIB. Gasses and redox sensors present a number of challenges to researchers in this area. The chemical state of these analytes can make it challenging to measure solution concentrations under many experimental conditions. This largely reflects the gaseous state of ethylene, CO, NO, and O2 as well as the high vapor pressure of H2S. A further challenge arises due to the speciation of the gasogens in solution via protonation or redox equilibria, leading to closely affiliated species such as NO− and O− 2 . As a result, correlating experimental conditions with concentration data requires a great deal of care. Each gasogen is toxic in high concentration, as can be anomalous redox poise, further challenging researchers to distinguish a gas/redox sensing response from a toxicity response. While binding or reacting with a gas may lead to chemical changes in metalloproteins, sensing requires some sort of output that alters cellular function. Identifying signal transduction adds a layer of complexity to gas and redox sensing. Furthermore, sensing is not typically due to conversion of a sensor between on/off states but rather arises from changes in the relative rates of competing pathways. This leads to serious debates over the physiological significance of gas-binding affinities when these values lay outside of the physiological range. The cross-talk between various gasogens, redox poise, and other nutrients is significant, with O2 a notable central player. This is partially due to the connection between pO2 and aerobic metabolism but addi-
http://dx.doi.org/10.1016/j.jinorgbio.2014.02.008 0162-0134/© 2014 Published by Elsevier Inc.
tionally arises due to the oxidation and reduction of some of the gasogens due either to direct reaction with O2 or with various redox agents within the cell. Furthermore, iron metabolism and O2 homeostasis are closely connected, making it a real challenge to isolate one variable from the other. Redox poise is a basal reporter on cellular metabolism, leading cells to adapt to changes in redox status. This likely plays an important role in proliferation and dormancy, due in part to changes in metabolic demands. It also plays a significant role in facultative organisms that can utilize multiple terminal electron acceptors, such as for chemolithotrophic organisms. The adaptation to redox poise may significantly impact the design and utility of microbial fuel cells, in which microbes must deliver electrons to an electrode surface rather than to a diffusible oxidant. Developing chemical tools to interrogate and manipulate gasogen concentrations and redox poise is currently of much interest. Such chemical tools are pushing our abilities to directly measure cellular activity in real time and are forming the basis for medical imaging and therapeutic agents. Although far from comprehensive, articles within this issue present selected approaches to these topics. The selection of review articles in this special issue provides different perspectives on the mechanisms of gas and redox sensing as well as on the biological and technological impacts of these sensory processes.
Michael J. Knapp Guest editor Department of Chemistry, University of Massachusetts, Amherst, Amherst, MA 01003, USA
