Molecular analysis of archael flagellins: similarity to the type IV pilin-transport superfamily widespread in bacteria.

Ultrastructural, biochemical and genetic evidence has shown that the flagella and flagellin proteins from members of the archaea are distinct from their bacterial counterparts. The most important evidence is the sequence dissimilarity between archael and bacterial flagellins. We report here similarity between archael flagellins and members of the bacterial type IV pilin-transport superfamily. In addition to sequence similarity, the archael flagellins and the type IV pilin-transport superfamily share an unusual signal sequence cleavage site and may have functional parallels. This relationship has important implications for the assembly and biogenesis of archael flagella.