The Archaeal Flagellum: A Novel Prokaryotic Motility Structure and the Role of Posttranslational Modifications in its Assembly and Function pp. 1-37
Authors: (Ken F. Jarrell, Department of Microbiology and Immunology, Queen’s University, Kingston, Ontario, Canada)
Abstract: The archaeal flagellum is a unique prokaryotic motility apparatus responsible for swimming that is found in all of the major cultured subgroupings of Archaea. While they are rotating structures like bacterial flagella, archaeal flagella nevertheless differ from their bacterial namesake in several fundamental ways. Indeed, archaeal flagella have more similarities to bacterial type IV pili, organelles responsible for a type of surface motility called twitching. Structurally, archaeal flagella are thinner than bacterial flagella and lack an internal channel large enough to allow passage of subunits. The flagellins in archaea are made as preproteins with type IV pilin-like signal peptides which are removed by a dedicated preflagellin peptidase homologous to the bacterial type IV prepilin peptidase. Both enzymes belong to a novel family of aspartic acid proteases with conserved aspartic acid residues that are necessary for signal peptide cleavage. Bacterial flagellins, on the other hand, are never made with signal peptides. Additional homologues have been identified between the archaeal flagella system and the type IV pilus system, including a conserved ATPase and a membrane component. A further posttranslational modification commonly found on archaeal flagellins is attachment of an N-linked glycan. This is again never seen in bacterial flagellins which can be, in rare cases, glycoproteins but always with the glycan attached in an O-linkage. Much recent data has accumulated on the assembly, biosynthesis and attachment of the N-glycan to archaeal flagellins and the important role that the glycan plays in flagella assembly and function.