ORDAL, George W.

Department of Biochemistry and College of Medicine
Ph.D. (1970) Stanford University

   Research Topics

   Research Interests  

   Signal transduction.  Research on our laboratory focuses on signal transduction.  We have chosen to explore chemotaxis in the bacterium Bacillus subtilis as a model system since it is readily subject to experimental manipulations.  The genome has been sequenced and we have identified, cloned and inactivated virtually all the chemotaxis genes and have purified many of the corresponding proteins.  We have a set of antibodies.  Thus, we are in a position to ask and answer a wide variety of experimental questions about the roles of each of the proteins, from the level of the biochemistry of individual proteins and their interactions to their respective roles in the behavior of the whole organism.

   Receptor complexes.  A general theme, employed by eucaryotes, is modulation of processes through large complexes of proteins, which may partly associate/disassociate, such as tyrosine kinase receptor complexes and transcription complexes.  However, the complexity is often very high and there is great difficulty substituting mutant alleles in vivo.  The B. subtilis chemotaxis system is a highly developed genetic system.  The receptor complex is a readily managed system, both in vivo and in vitro, for understanding the dynamics of complex interactions how these interactions can lead to the appropriate output over a broad dynamic range.  We know from yeast two-hybrid experiments many of the pairwise interactions

   Signal creation and amplification.  Chemotaxis is based on the traditional two-component system.  An autophosphorylating kinase senses the system “input” by sensing changes in receptor conformation caused by binding attractants or repellents.  This allows phosphorylation of a response regulator so that direction of flagellar rotation can be controlled (the “output”).  Unstimulated receptors may form an array of α-helices and the allosteric state of that array may govern output.  We are trying to understand how signals are transduced through the membrane by studying the movement of there receptor α-helices by using crosslinking of strategically placed Cys residues.  We are also trying to explore how receptor interactions greatly expand the range over which the bacteria are sensitive to environmental stimuli by characterizing strains where some receptors have been eliminated and others selectively modified at the sites of methylation.

   Extinguishing signals.  Chemotaxis is one of the few sensory systems in prokaryotes where adaptation occurs so that continuing presence of attractant no longer affects output from the receptor complex.  We are trying to identify each of the several processes that affect adaptation and how they work.  We have found that one of the unique proteins, found also in the archaea but not in E. coli, the regulatory protein CheC, plays an important role.  Another unique protein, CheV, appears to facilitate adaptation only when phosphorylated and we are trying to understand how it does it.  Selective methylation and demethylation of particular sites on receptors seems to be necessary for excitation and for adaptation in some instances, and we are trying to understand the types of changes in interactions with other chemotaxis proteins are involved in this.

   Unique proteins.  The paradigm organism for chemotaxis has historically been E. coli.  However, two proteins that play very important roles in chemotaxis—CheC and CheD—are not present there but are present in the archaea.  The receptors are also larger in B.subtilis and in the archaea than in E. coli, and receptor methylation is handled differently.  Thus, the ancestral mechanism and the mechanism still present in modified form in most archaea and bacteria might be closer to the mechanism in B. subtilis than to that in E. coli.  The heart of understanding this mechanism is understanding CheC and CheD and another protein, also not found in E. coli but found elsewhere, CheV.  We are trying to understand how they each function by a combination of genetic and biochemical approaches.  We have expressed wild type and genetically modified versions of virtually all the chemotaxis proteins and are investigating their activities and interactions both in vivo and in vitro.

   Key Words   Recombinant DNA, DNA-Protein Interactions, Molecular Evolution, Genome Organization/RFLP Mapping, Fermentation, Microbial Physiology, Site-Directed Mutagenesis, Membrane Structure and Function, Protein Purification and Characterization, Protein Processing and Secretion, Active Sites and Receptors

   Current Research Funding   NIH

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