Kinetic analysis of the synthesis and assembly of type 1 fimbriae of Escherichia coli

Abstract

The adhesive organelles (type 1 fimbriae) of K-12 and other isolates of Escherichia coli are composed of identical 17,000-dalton subunits. We examined the assembly of these subunits into fimbrial organelles. After synthesis, the nascent subunits were first processed and then assembled into the organelles; the assembly step took almost 3 min in log-phase cultures at 37°C. Even during blockage of protein synthesis, the free subunits continued to assemble until the pool was depleted. This pool was small in comparison with the amount of total fimbrial protein already assembled into surface organelles and was not sufficient to regenerate new detectable organelles after the removal of preexistent ones by blending. Assembly appeared to slow when the metabolic rate of the bacterial cells slowed, since subunits took longer to appear in the organelles at lower than optimal temperatures or as a culture entered the stationary phase. The synthetic rate of subunits slowed sooner than that of total cellular proteins as a culture approached the stationary phase and ceased completely as the culture entered the stationary phase. The amount of fimbrial antigen expressed on the surface of the cells remained relatively constant during growth of a culture. Type 1 fimbriae (or pili) are proteinaceous appendages 7 nm in width projecting from the surface of many gram-negative bacteria (4). They consist of aggregates of helically arranged identical 17,000-dalton polypeptides with 3.

Role of Pili (Fimbriae) in Attachment of Bradyrhizobium japonicum to Soybean Roots

“…Blending of Bradyrhizobium cultures reduced their attachment capacity by approximately 90% ( Table 2). The kinetics of reacquisition of Bradyrhizobium attachment capacity was similar to the kinetics of pilus synthesis by a blended culture of Escherichia coli (16). Chloramphenicol treatment, which completely inhibited the synthesis of type 1 (attachment) pili in E. coli (16), also eliminated the reacquisition of the attachment capacity of a blended Bradyrhizobium suspension ( Table 2).…”

Mechanism of fibre assembly through the chaperone–usher pathway

“…It is thus conceivable that DSE occurs in a concerted manner also in the presence of the usher in vivo. Pilus assembly in vivo occurs within minutes (Dodd & Eisenstein, 1984), whereas DSE proceeds on a timescale of hours in vitro (Fig 2). It is therefore likely that the usher catalyses DSE in vivo.…”

Export and secretion of proteins by bacteria

“…The subunits seem to accumulate in the periplasm before they are translocated to the outer membrane, and it seems likely that the additional gene products are required for this final stage of export. Polymerisation of type I fimbriae from a relatively small intracellular pool takes about 3 min, and is considerably delayed when metabolic activity is reduced [380]. These fimbrial subunits may also have signal peptides, and seem to be channeled into the normal signal peptide pathway for protein export [381] (section 3).…”