Direct demonstration that homotetrameric chaperone SecB undergoes a dynamic dimer-tetramer equilibrium

We have shown here that the cytosolic bacterial chaperone SecB is a structural dimer of dimers that undergoes a dynamic equilibrium between dimer and tetramer in the native state. We demonstrated this equilibrium by mixing two tetrameric species of SecB that can be distinguished by size. We showed that the homotetrameric species exchanged dimers, because when the mixture was analyzed both by size exclusion chromatography and native polyacrylamide gel electrophoresis a third hybrid tetrameric species was detected. Furthermore, treatment of SecB with 5,5'-dithiobis-(2-nitrobenzoic acid), which modifies the sulfhydryl group on cysteines, caused irreversible dissociation to a dimer indicating that cysteine must be involved in the stabilizing interactions at the dimer interface. It is clear that the two dimer-dimer interfaces of the SecB tetramer are differentially stable. Dissociation at one interface allows for a dynamic dimer-tetramer equilibrium. Because only dimers were exchanged it is clear that the other interface between dimers is significantly more stable, otherwise oligomers should have formed with a random distribution of monomers

Genomics of quality traits

The quality attributes of cereal grains are valued in the context of a complex food chain that integrates outputs achievable by breeding, production, and processing. New processing technologies, environmental change, and changes in consumer preferences demand that quality attributes of wheat and barley need to be continually modified. The advances in the genomics of quality described in this chapter provide the basis for ensuring that the genetic approaches encompassing the complexities of the gene networks underpinning quality attributes can meet the challenges presented by the rapid changes occurring within the food chain