Amino acid residue Ala‐62 in the FimH fimbrial adhesin is critical for the adhesiveness of meningitis‐associated Escherichia coli to collagens

Abstract

SummaryAdhesion of meningitis-associated Escherichia coli O18acK1H7 to collagens was characterized. The E. coli strain IHE 3034 adhered to type IV and type I collagens but not to type III collagen immobilized on glass. Collagens lack terminal mannosyl units, yet the bacterial adhesion was completely abolished in the presence of ␣-methyl-D-mannoside. A cat cassette was introduced into the fimA gene of IHE 3034, and the resulting mutant strain IHE 3034-2 failed to adhere to collagens. In contrast, insertion of a Gm cassette into the sfaA gene of IHE 3034, encoding the S-fimbrillin, had no significant effect on the adhesiveness. The fim cluster from IHE 3034 was cloned and expressed in trans in the fimA::cat mutant strain IHE 3034-2. The complemented strain IHE 3034-2(pRPO-1) exhibited adhesiveness to type IV and type I collagens, confirming the function of the type 1 fimbria in the adhesion. We have previously shown that the type 1 fimbria from E. coli K-12 strain PC31 does not confer bacterial adhesiveness to collagens. The fimH genes from E. coli IHE 3034 as well as from PC31 were expressed in the fimH-null strain MS4. The FimH from IHE 3034 potentiated collagen adherence, whereas the FimH from PC31 was inactive. Sequence comparison of fimH from IHE 3034 and PC31 revealed five amino-acid differences in the predicted mature FimH proteins: at residues 27, 62, 70, 78 and 201. Each of these residues in the IHE 3034-FimH were individually substituted to the corresponding amino acid in the PC31-FimH. The substitution S62→A completely abolished collagen adhesiveness. The reverse substitution A62→S in the PC31-FimH as well as in the FimH from another E. coli strain induced collagen adhesiveness to the level seen with IHE 3034-FimH. Out of nine fimH genes analysed from isolates of E. coli, collagen adhesiveness as well as alanine at position 62 in FimH were found only in two O18acK1H7 isolates with the isoenzyme profile ET type 1. Our results demonstrate that the amino-acid residue Ala-62 in the FimH lectin is critical for the adhesion to collagens by a highly virulent clonal group of E. coli.

Positive selection identifies an in vivo role for FimH during urinary tract infection in addition to mannose binding

“…Surprisingly, in vivo, the A62S-ON strain (compared to a wt-ON control strain) rescued the CFUs/bladder phenotype at 24 hpi seen with the A62S mutant. Therefore, the in vitro mannose-binding defect of A62S is a result of altered FimH function (36,48), while the in vivo fitness defect of A62S is due to altered fim regulation.…”

“…None of the PSAA was located near the conserved mannose-binding pocket of FimH, and examination of the crystal structure of the FimC-FimH-mannose complex revealed no obvious relationship between PSAA mutations and mannose binding. Allosteric effects of FimH mutations have been described and may account for the decreased mannose binding of the A62S mutant (36,48). However, no structural basis for the severe in vivo fitness defect of the A27V/V163A double mutation is apparent.…”

Sequence analysis demonstrates the conservation of fimH and variability of fimA throughout Avian Pathogenic Escherichia coli (APEC)

“…Pouttu et al [16] demonstrated that the presence of a serine at position 62 of the mature FimH (instead of alanine) completely abolishes binding of E. coli to collagen. All investigated APEC strains and the human AF288194 strain showed a serine at position 62 that could correspond to a lack of collagen binding.…”

“…The FimH adhesin has been described to be conserved throughout several strains of E. coli and even other F1 fimbriated Enterobacteriaceae [2]. Several important amino acids in the protein have been identified and extensively analysed [16,20,21]. On the contrary, the FimA major protein has been reported to be variable between the different strains of E. coli [2].…”

Comparative genome analysis of the α-proteobacteria: Relationships between plant and animal pathogens and host specificity

“…These point mutations may lead to truncations or frameshifts in genes that may play a role in host-pathogen interactions. Finally, the role of point mutations that change the amino acid sequence of a protein should also be considered, as it has been shown that a single amino acid change in the E. coli FimH adhesin leads to loss of collagen-binding activity (20). Some of the variable surface proteins identified in the comparative genome analysis of B. suis and B. melitensis, therefore, may be additional candidates for host-specific virulence factors.…”