Linn AK, Samainukul N, Sakdee S, Butnampetch C, Li HC, Angsuthanasombat C, Katzenmeier G. N-Terminally Added Tag Selectively Enhances Heterologous Expression of VacA Cytotoxin Variants from Helicobacter pylori.
Protein Pept Lett 2021;
28:643-650. [PMID:
33183185 DOI:
10.2174/0929866527666201112122831]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 09/18/2020] [Accepted: 09/28/2020] [Indexed: 11/22/2022]
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.
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