Multidomain of flagellin

Scanning microcalorimetric and circular dichroism studies of the normal and mutant flagellins of Salmonella suggest that they have a multidomain structure in common. Flagellin polymers (flagella) are depolymerized irreversibly into monomers as the temperature is raised, and the monomers undergo denaturation reversibly when cooled and heated again. The calorimetric enthalpy of this reversible process is twice as large as the van't Hoff enthalpy, suggesting that flagellin monomers contain two co-operative regions that melt independently at the same temperature. In all flagellin specimens examined, the ellipticity at 222 nm of polymers at room temperature is 1.6 times as large as that of monomers, and the dependence of ellipticity on temperature takes place in the same temperature intervals in which calorimetric effects take place. From these results, we propose that flagellin molecules consist of several domains, two of which are distinctly structured in monomers at room temperature, while the others acquire more regular structures during polymerization.