N-Terminally Added Tag Selectively Enhances Heterologous Expression of VacA Cytotoxin Variants from Helicobacter pylori

Author(s): Aung Khine Linn, Nitchakan Samainukul, Somsri Sakdee, Chonthicha Butnampetch, Hui-Chun Li, Chanan Angsuthanasombat*, Gerd Katzenmeier

Journal Name: Protein & Peptide Letters

Volume 28 , Issue 6 , 2021


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Graphical Abstract:


Abstract:

Background: Gastric pathogen Helicobacter pylori secretes VacA cytotoxin displaying a high degree of polymorphic variations of which the highest VacA pathogenicity correlates with m1-type variant followed by VacA-m2.

Objective: To comparatively evaluate expression in Escherichia coli of the mature VacA variants (m1- and m2-types) and their 33- and 55/59-kDa domains fused with His(6) tag at N- or C-terminus.

Methods: All VacA clones expressed in E. coli TOP10™ were analyzed by SDS-PAGE and Western blotting. VacA inclusions were solubilized under native conditions (~150-rpm shaking at 37°C for 2 h in 20 mM HEPES (pH7.4) and 150 mM NaCl). Membrane-perturbing and cytotoxic activities of solubilized VacA proteins were assessed via liposome-entrapped dye leakage and resazurin- based cell viability assays, respectively. VacA binding to human gastric adenocarcinoma cells was assessed by immunofluorescence microscopy. Side-chain hydrophobicity of VacA was analyzed through modeled structures constructed by homology- and ab initio-based modeling.

Results: Both full-length VacA-m1 and 33-kDa domain were efficiently expressed only in the presence of N-terminal extension while its 55-kDa domain was capably expressed with either N- or Cterminal extension. Selectively enhanced expression was also observed for VacA-m2. Protein expression profiles revealed a critical period in IPTG-induced production of the 55-kDa domain with N-terminal extension unlike its C-terminal extension showing relatively stable expression. Both VacA- m1 isolated domains were able to independently bind to cultured gastric cells similar to the full- length toxin, albeit the 33-kDa domain exhibited significantly higher activity of membrane perturbation than others. Membrane-perturbing and cytotoxic activities observed for VacA-m1 appeared to be higher than those of VacA-m2. Homology-based modeling and sequence analysis suggested a potential structural impact of non-polar residues located at the N-terminus of the mature VacA toxin and its 33-kDa domain.

Conclusion: Our data provide molecular insights into selective influence of the N-terminally added tag on efficient expression of recombinant VacA variants, signifying biochemical and biological implications of the hydrophobic stretch within the N-terminal domain.

Keywords: Cell viability assay, His(6) tag, human gastric cell, hydrophobic stretch, inclusion solubilization, membrane perturbation.

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Article Details

VOLUME: 28
ISSUE: 6
Year: 2021
Published on: 12 November, 2020
Page: [643 - 650]
Pages: 8
DOI: 10.2174/0929866527666201112122831
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