title: Structural independence of conjugative coupling protein TrwB from its Type IV secretion machinery.
abstract: The stability of components of multiprotein complexes often relies on the presence of the functional complex. To assess structural dependence among the components of the R388 Type IV secretion system (T4SS), the steady-state level of several Trw proteins was determined in the absence of other Trw components. While several Trw proteins were affected by the lack of others, we found that the coupling protein TrwB is not affected by the absence of other T4SS components, nor did its absence alter significantly the levels of integral components of the complex, underscoring the independent role of the coupling protein on the T4SS architecture. The cytoplasmic ATPases TrwK (VirB4) and TrwD (VirB11) were affected by the absence of several core complex components, while the pilus component TrwJ (VirB5) required the presence of all other Trw proteins (except for TrwB) to be detectable. Overall, the results delineate a possible assembly pathway for the T4SS of R388. We have also tested structural complementation of TrwD (VirB11) and TrwJ (VirB5) by their homologues in the highly related Trw system of Bartonella tribocorum (Bt). The results reveal a correlation with the functional complementation data previously reported.
authors.affiliation: Departamento de Biología Molecular, Universidad de Cantabria, and IBBTEC-UC, CSIC, SODERCAN, Santander, Spain.
authors.forename: Delfina
authors.initials: D
authors.lastname: Larrea
authors.forename: Héctor D
authors.initials: HD
authors.lastname: de Paz
authors.forename: Ignacio
authors.initials: I
authors.lastname: Arechaga
authors.forename: Fernando
authors.initials: F
authors.lastname: de la Cruz
authors.forename: Matxalen
authors.initials: M
authors.lastname: Llosa
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001473:Bartonella / Q000235:genetics / Q000378:metabolism; D003227:Conjugation, Genetic; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000235:genetics* / Q000378:metabolism; D005816:Genetic Complementation Test; D009876:Operon; D010957:Plasmids / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D000251:Adenosine Triphosphatases