Ammonia transport (Amt) proteins and Rhesus (Rh) proteins are the only two identified biological gas channels among organisms. Rh proteins, which are best known as antigens on human red blood cells, are gas channels for CO2. They are required for optimal growth of the green alga Chlamydomonas reinhardtii at high C02. Amt proteins, which are known as the-ancestral homolog to Rh proteins, are gas channels for NH3. They are required for optimal growth of enteric bacteria Escherichia coli and Salmonella typhimurium at low NH3. Since phospholipid bilayers of the cell membrane are permeable to the gas species, the reason why gas channels are needed by cells is not known. Physiological studies in E. coli and S. typhimurium show that at low NH3 concentrations NH3 transport by AmtB appears to be coupled to glutamine synthetase which assimilates NH3 into glutamine. Therefore, in this proposal we seek to understand how AmtB in E. coli is functionally coupled to glutamine synthetase and hypothesize that AmtB and glutamine synthetase associate physically. The physical contact between AmtB and glutamine synthetase may allow the direct delivery of NH3 from the pore of AmtB to the active site of glutamine synthetase and hence increase the rate of assimilation of NH3. One of the two specific aims of this proposal is to identify amino acid mutations in AmtB that impair growth and ammonium uptake activity at low NH3. These amtB mutations should not cause global protein misfolding of AmtB or loss of function of the pore of AmtB but rather locally affect cytoplasmic regions of the protein that are its binding site for glutamine synthetase. The second specific aim is to test the association between AmtB and GS using molecular biology and genetics approaches. II. Relevance: This proposed study of E. coli AmtB will enable us to gain a better understanding of how gas channels work to help maintain healthy cell physiology. Knowing gas channel function will help us identify the basis of dysfunction in human disease such as Rh null disease.
|Liu, Min; Hsu, Joanne; Chan, Caleb et al. (2012) The ubiquitin ligase Siah1 controls ELL2 stability and formation of super elongation complexes to modulate gene transcription. Mol Cell 46:325-34|