Volume change associated with the G-F transformation of flagellin

Abstract

The volume change of the solution, Δ V, associated with the polymerization at neutral pH of the protein, flagellin, to flagella, a typical G-F transformation, was measured with a Carlsberg-type dilatometer. A large positive volume change, greater than 150 ml. per mole of flagellin polymerized, was observed for this process. The effect of variations in protein concentration and temperature on Δ V was studied. Both the final value of Δ V observed after complete polymerization of flagellin had occurred, Δ V max, as well as the rate of the volume change on polymerizing flagellin, estimated as the reciprocal of the mid-plateau value ( tΔ V max 2) −1 , were found to be temperature-dependent. Between 22 and 28 °C the polymerization, rate increased with increasing temperature. However, over this temperature range ΔV max was unchanged and had a value of 157 ± 4 ml. per mole of flagellin polymerized. Above 28 °C the polymerization rate decreased with increasing temperature but ΔV max increased to a maximum value at 35 °C of 306 ml. per mole of flagellin polymerized. At temperatures higher than 35 °C, the rate for the volume change decreases markedly and polymerization, as measured by changes in specific viscosity, does not occur. The effect of increasing temperature on the rate and magnitude of the volume changes observed is explained by assuming that the protein can be reversibly transformed to a state which lacks the capacity to reconstitute flagella, and that at temperatures above 28 °C this transformation becomes rate limiting for the polymerization process. Such a reversible transformation of flagellin can explain some of the well-known effects of temperature on the expression of motility and the formation of flagella in vivo.