A Seventh-day Adventist Organization

Mark Johnson, PhD

Associate Professor

Basic Sciences
Division of Microbiology
School of Medicine
Loma Linda University
Loma Linda, CA 92350
U.S.A

Phone:(909) 558-2765
Fax:(909) 558-4035
E-mail: mjohnson@llu.edu

Profile Photo

Research Interest

Trained in classical enzymology and protein chemistry, my current focus is on how Escherichia coli senses energy generated by the electron transport chain, and signals this status to the chemotaxis cascade. All organisms struggle constantly to avoid thermodynamic equilibration or "cell death." To do this, they generate impressive amounts of energy by metabolizing chemicals (food) or by transducing light energy into high energy chemicals. The lowly single-celled bacterium must not only find food, but also a way to optimize the metabolism of the food. It is no surpise then, that some motile bacteria have a means by which to migrate towards higher concentrations of chemical foods (chemotaxis), as well as towards higher concentrations of oxygen (aerotaxis) or other electron acceptors for more energetic combustion of the food. We co-discovered an oxygen receptor in Escherichia coli that we named Aer (for aero-, energy- and redox taxis; see Rebbapragada et al., 1997). Our data suggests that this sensor monitors the energy production of the electron transport system and signals this status to the flagellar motor through the chemotaxis cascade. Some critical questions we are pursuing include: What component(s) of energy production (PMF; electron transport; redox state) does this sensor monitor? With what component(s) of the electron transport chain does this receptor interact? What is the quaternary structure? What is the topology of the receptor? What conformational changes occur on signaling? What interactions occur between the sensing region and the signaling region? What can this receptor tell us about oxygen sensing in higher organisms?

Selected Publications

  1. Garcia D, Watts KJ, Johnson MS and Taylor BL. (2016) Delineating PAS-HAMP interaction surfaces and signalling-associated changes in the aerotaxis receptor Aer. Mol Microbiol 100:156-72.
  2. Watts KJ, Johnson MS, and Taylor BL. (2011) Different Conformations of the Kinase-on and Kinase-Off Signaling States in the Aer HAMP Domain. J Bacteriol. 193:4095-4103.
  3. Campbell AJ, Watts KJ, Johnson MS, and Taylor BL. (2011) Role of the F1 region in the Escherichia coli aerotaxis receptor Aer. J Bacteriol 193:358-66.
  4. Watts KJ, Taylor BL, and Johnson MS. (2011) PAS/poly-HAMP signalling in Aer-2, a soluble haem-based sensor. Mol Microbiol 79:686-99.
  5. Campbell AJ, Watts KJ, Johnson MS, Taylor BL. (2010) Gain-of-function mutations cluster in distinct regions associated with the signalling pathway in the PAS domain of the aerotaxis receptor, Aer. Mol Microbiol. 77(3):575-86.
  6. Watts KJ, Johnson MS, Taylor BL.(2008) Structure-function relationships in the HAMP and proximal signaling domains of the aerotaxis receptor Aer. J Bacteriol. 190(6):2118-27.
  7. Amin DN, Taylor BL, Johnson MS. (2007) Organization of the aerotaxis receptor aer in the membrane of Escherichia coli. J Bacteriol. 189(20):7206-12.
  8. Taylor BL, Watts KJ, Johnson MS. (2007) Oxygen and redox sensing by two-component systems that regulate behavioral responses: behavioral assays and structural studies of aer using in vivo disulfide cross-linking. Methods Enzymol. 422:190-232.
  9. Edwards JC, Johnson MS, Taylor BL. (2006) Differentiation between electron transport sensing and proton motive force sensing by the Aer and Tsr receptors for aerotaxis. Mol Microbiol. 62(3):823-37.
  10. Watts KJ, Sommer K, Fry SL, Johnson MS, Taylor BL. (2006) Function of the N-terminal cap of the PAS domain in signaling by the aerotaxis receptor Aer. J Bacteriol. 188(6):2154-62.
  11. Watts KJ, Johnson MS, Taylor BL. (2006) Minimal requirements for oxygen sensing by the aerotaxis receptor Aer. Mol Microbiol. 59(4):1317-26.
  12. Amin DN, Taylor BL, Johnson MS. (2006) Topology and boundaries of the aerotaxis receptor Aer in the membrane of Escherichia coli. J Bacteriol. 188(3):894-901.
  13. Ma Q, Johnson MS, Taylor BL. (2005) Genetic analysis of the HAMP domain of the Aer aerotaxis sensor localizes flavin adenine dinucleotide-binding determinants to the AS-2 helix. J Bacteriol. 187(1):193-201.
  14. Ma Q, Roy F, Herrmann S, Taylor BL, Johnson MS. (2004) The Aer protein of Escherichia coli forms a homodimer independent of the signaling domain and flavin adenine dinucleotide binding. J Bacteriol. 186(21):7456-9.
  15. Watts KJ, Ma Q, Johnson MS, Taylor BL. (2004) Interactions between the PAS and HAMP domains of the Escherichia coli aerotaxis receptor Aer. J Bacteriol. 86(21):7440-9.
  16. Herrmann S, Ma Q, Johnson MS, Repik AV, Taylor BL. (2004) PAS domain of the Aer redox sensor requires C-terminal residues for native-fold formation and flavin adenine dinucleotide binding. J Bacteriol. 186(20):6782-91
  17. Yu HS, Saw JH, Hou S, Larsen RW, Watts KJ, Johnson MS, Zimmer MA, Ordal GW, Taylor BL, Alam M. (2002) Aerotactic responses in bacteria to photoreleased oxygen. FEMS Microbiol Lett. 217(2):237-42.
  18. Taylor BL, Rebbapragada A, Johnson MS. (2001) The FAD-PAS domain as a sensor for behavioral responses in Escherichia coli. Antioxid Redox Signal. 3(5):867-79. Review.