Journal of Molecular Biology
Volume 64, Issue 1, 28 February 1972, Pages 251-256, IN17-IN25, 257-268
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Polymorphism of Salmonella flagella as investigated by means of in vitro copolymerization of flagellins derived from various strains

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Abstract

At physiological ionic strength and pH, two kinds of monomeric flagellins derived from different Salmonella strains may copolymerize into long filaments which, like intact flagella, assume wave-forms in electron microscope observations. In this study we carried out quantitative and statistical analyses of wave-forms assumed by various kinds of copolymers, using two kinds of normally flagellated strains SJ670 (i) and SJ25 (n), a curly flagellar mutant SJ30 (c) and a straight flagellar mutant SJ814 (s). The wave-form of copolymer was represented in terms of the contour length of filament contained in one period, L, and the wave-height, h.

Usually, homogeneous polymers of i- and n-flagellins assume the large-period normal wave-form and that of s-flagellin assumes the straight form. In combinations of (i+s) and (n+s), it was found that the wave-form of copolymer became smaller in both L and h as the ratio of mixed s-monomer increased. This change of wave-form was shown to occur in a stepwise manner: between the normal and straight forms three stable intermediates appeared, which are referred to as types II, III and IV, respectively. In each stable form copolymers (i+s) and (n+s) were closely similar with respect to both L and h. These copolymers thus assumed five common stable forms depending on the ratio of constituent flagellins.

Homogeneous polymers of c-flagellin assumed two types of waves, referred to as II′ and III′. Waves II′ and III′ had approximately equal values of L to waves II and III, respectively, whilst the former two waves had a larger value of h than the latter two. In the investigation of copolymers (i+c) or (c+s), it was found that when the ratio of mixed c-monomer was gradually increased, the change of wave-form from type II to II′ or type III to III′ took place in a continuous manner. For this reason, the relationship between waves II and II′ or waves III and III′ is regarded as homologous.

In order to understand the polymorphism of copolymers described here, it will be necessary to consider that homogeneous polymers themselves are polymorphic and, depending on environmental conditions, capable of assuming several stable forms homologous to those which have been associated with copolymers. From this point of view, the polymorphic nature of bacterial flagella will be discussed.

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