title: Heterologous assembly of type IV pili by a type II secretion system reveals the role of minor pilins in assembly initiation.
abstract: In Gram-negative bacteria, type IV pilus assembly (T4PS) and type II secretion (T2SS) systems polymerize inner membrane proteins called major pilins or pseudopilins respectively, into thin filaments. Four minor pilins are required in both systems for efficient fibre assembly. Escherichia coli K-12 has a set of T4PS assembly genes that are silent under standard growth conditions. We studied the heterologous assembly of the E. coli type IV pilin PpdD by the Klebsiella oxytoca T2SS called the Pul system. PpdD pilus assembly in this context depended on the expression of the K. oxytoca minor pseudopilin genes pulHIJK or of the E. coli minor pilin genes ppdAB-ygdB-ppdC. The E. coli minor pilins restored assembly of the major pseudopilin PulG in a pulHIJK mutant, but not the secretion of the T2SS substrate pullulanase. Thus, minor pilins and minor pseudopilins are functionally interchangeable in initiating major pilin assembly, further extending the fundamental similarities between the two systems. The data suggest that, in both systems, minor pilins activate the assembly machinery through a common self-assembly mechanism. When produced together, PulG and PpdD assembled into distinct homopolymers, establishing major pilins as key determinants of pilus elongation and structure.
authors.affiliation: Molecular Genetics Unit, Department of Microbiology, Institut Pasteur, 75015, Paris, France.
authors.forename: David A
authors.initials: DA
authors.lastname: Cisneros
authors.forename: Gerard
authors.initials: G
authors.lastname: Pehau-Arnaudet
authors.forename: Olivera
authors.initials: O
authors.lastname: Francetic
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics*; D048168:Escherichia coli K12 / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D041121:Klebsiella oxytoca / Q000201:enzymology* / Q000235:genetics; D046911:Macromolecular Substances / Q000378:metabolism*; D055503:Protein Multimerization; D021122:Protein Subunits
chemical_list: D058947:Bacterial Secretion Systems; D046911:Macromolecular Substances; D021122:Protein Subunits; D036781:Fimbriae Proteins