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Comparison of the functional properties of trimeric and monomeric CaiT of Escherichia coli.

ABSTRACT: Secondary transporters exist as monomers, dimers or higher state oligomers. The significance of the oligomeric state is only partially understood. Here, the significance of the trimeric state of the L-carnitine/?-butyrobetaine antiporter CaiT of Escherichia coli was investigated. Amino acids important for trimer stability were identified and experimentally verified. Among others, CaiT-D288A and -D288R proved to be mostly monomeric in detergent solution and after reconstitution into proteoliposomes, as shown by blue native gel electrophoresis, gel filtration, and determination of intermolecular distances. CaiT-D288A was fully functional with kinetic parameters similar to the trimeric wild-type. Significant differences in amount and stability in the cell membrane between monomeric and trimeric CaiT were not observed. Contrary to trimeric CaiT, addition of substrate had no or only a minor effect on the tryptophan fluorescence of monomeric CaiT. The results suggest that physical contacts between protomers are important for the substrate-induced changes in protein fluorescence and the underlying conformational alterations.

SUBMITTER: Bracher S

PROVIDER: S-EPMC6406002 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Comparison of the functional properties of trimeric and monomeric CaiT of Escherichia coli.

Bracher Susanne S Hilger Daniel D Guérin Kamila K Polyhach Yevhen Y Jeschke Gunnar G Krafczyk Ralph R Giacomelli Giacomo G Jung Heinrich H

Scientific reports 20190307 1

Secondary transporters exist as monomers, dimers or higher state oligomers. The significance of the oligomeric state is only partially understood. Here, the significance of the trimeric state of the L-carnitine/γ-butyrobetaine antiporter CaiT of Escherichia coli was investigated. Amino acids important for trimer stability were identified and experimentally verified. Among others, CaiT-D288A and -D288R proved to be mostly monomeric in detergent solution and after reconstitution into proteoliposom ...[more]

PMID: 30846799

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Project description:Urinary tract infections (UTIs) are associated with high rates of morbidity and mortality worldwide, and uropathogenic Escherichia coli (UPEC) is the main etiologic agent. Fimbriae assembled on the bacterial surface are essential for adhesion to the urinary tract epithelium. In this study, the FimH, CsgA, and PapG adhesins were fused to generate biomolecules for use as potential target vaccines against UTIs. The fusion protein design was generated using bioinformatics tools, and template fusion gene sequences were synthesized by GenScript in the following order fimH-csgA-papG-fimH-csgA (fcpfc) linked to the nucleotide sequence encoding the [EAAAK]5 peptide. Monomeric (fimH, csgA, and papG), dimeric (fimH-csgA), and trimeric (fimH-csgA-papG) genes were cloned into the pLATE31 expression vector and generated products of 1040, 539, 1139, 1442, and 2444 bp, respectively. Fusion protein expression in BL21 E. coli was induced with 1 mM IPTG, and His-tagged proteins were purified under denaturing conditions and refolded by dialysis using C-buffer. Coomassie blue-stained SDS-PAGE gels and Western blot analysis revealed bands of 29.5, 11.9, 33.9, 44.9, and 82.1 kDa, corresponding to FimH, CsgA, PapG, FC, and FCP proteins, respectively. Mass spectrometry analysis by MALDI-TOF/TOF revealed specific peptides that confirmed the fusion protein structures. Dynamic light scattering analysis revealed the polydispersed state of the fusion proteins. FimH, CsgA, and PapG stimulated the release of 372-398 pg/mL IL-6; interestingly, FC and FCP stimulated the release of 464.79 pg/mL (p ≤ 0.018) and 521.24 pg/mL (p ≤ 0.002) IL-6, respectively. In addition, FC and FCP stimulated the release of 398.52 pg/mL (p ≤ 0.001) and 450.40 pg/mL (p ≤ 0.002) IL-8, respectively. High levels of IgA and IgG antibodies in human sera reacted against the fusion proteins, and under identical conditions, low levels of IgA and IgG antibodies were detected in human urine. Rabbit polyclonal antibodies generated against FimH, CsgA, PapG, FC, and FCP blocked the adhesion of E. coli strain CFT073 to HTB5 bladder cells. In conclusion, the FC and FCP proteins were highly stable, demonstrated antigenic properties, and induced cytokine release (IL-6 and IL-8); furthermore, antibodies generated against these proteins showed protection against bacterial adhesion.

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Comparison of the functional properties of trimeric and monomeric CaiT of Escherichia coli.

Publications

Comparison of the functional properties of trimeric and monomeric CaiT of Escherichia coli.

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