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Rodnin MV, Vasques-Montes V, Kyrychenko A, Oliveira NFB, Kashipathy MM, Battaile KP, Douglas J, Lovell S, Machuqueiro M, Ladokhin AS. Histidine Protonation and Conformational Switching in Diphtheria Toxin Translocation Domain. Toxins (Basel) 2023; 15:410. [PMID: 37505680 PMCID: PMC10467104 DOI: 10.3390/toxins15070410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 06/06/2023] [Accepted: 06/21/2023] [Indexed: 07/29/2023] Open
Abstract
Protonation of key histidine residues has been long implicated in the acid-mediated cellular action of the diphtheria toxin translocation (T-) domain, responsible for the delivery of the catalytic domain into the cell. Here, we use a combination of computational (constant-pH Molecular Dynamics simulations) and experimental (NMR, circular dichroism, and fluorescence spectroscopy along with the X-ray crystallography) approaches to characterize the initial stages of conformational change happening in solution in the wild-type T-domain and in the H223Q/H257Q double mutant. This replacement suppresses the acid-induced transition, resulting in the retention of a more stable protein structure in solutions at pH 5.5 and, consequently, in reduced membrane-disrupting activity. Here, for the first time, we report the pKa values of the histidine residues of the T-domain, measured by NMR-monitored pH titrations. Most peaks in the histidine side chain spectral region are titrated with pKas ranging from 6.2 to 6.8. However, the two most up-field peaks display little change down to pH 6, which is a limiting pH for this protein in solution at concentrations required for NMR. These peaks are absent in the double mutant, suggesting they belong to H223 and H257. The constant-pH simulations indicate that for the T-domain in solution, the pKa values for histidine residues range from 3.0 to 6.5, with those most difficult to protonate being H251 and H257. Taken together, our experimental and computational data demonstrate that previously suggested cooperative protonation of all six histidines in the T-domain does not occur.
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Affiliation(s)
- Mykola V. Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
| | - Victor Vasques-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
| | - Alexander Kyrychenko
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, 61022 Kharkiv, Ukraine
| | - Nuno F. B. Oliveira
- Institute of Biosystems and Integrative Sciences, University of Lisbon, 1749-016 Lisbon, Portugal (M.M.)
| | - Maithri M. Kashipathy
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66047, USA (S.L.)
| | | | - Justin Douglas
- COBRE Bio-NMR Laboratory, University of Kansas, Lawrence, KS 66045, USA;
| | - Scott Lovell
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66047, USA (S.L.)
| | - Miguel Machuqueiro
- Institute of Biosystems and Integrative Sciences, University of Lisbon, 1749-016 Lisbon, Portugal (M.M.)
| | - Alexey S. Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
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Zuzic L, Marzinek JK, Anand GS, Warwicker J, Bond PJ. A pH-dependent cluster of charges in a conserved cryptic pocket on flaviviral envelopes. eLife 2023; 12:82447. [PMID: 37144875 PMCID: PMC10162804 DOI: 10.7554/elife.82447] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 04/18/2023] [Indexed: 05/06/2023] Open
Abstract
Flaviviruses are enveloped viruses which include human pathogens that are predominantly transmitted by mosquitoes and ticks. Some, such as dengue virus, exhibit the phenomenon of antibody-dependent enhancement (ADE) of disease, making vaccine-based routes of fighting infections problematic. The pH-dependent conformational change of the envelope (E) protein required for fusion between the viral and endosomal membranes is an attractive point of inhibition by antivirals as it has the potential to diminish the effects of ADE. We examined six flaviviruses by employing large-scale molecular dynamics (MD) simulations of raft systems that represent a substantial portion of the flaviviral envelope. We utilised a benzene-mapping approach that led to a discovery of shared hotspots and conserved cryptic sites. A cryptic pocket previously shown to bind a detergent molecule exhibited strain-specific characteristics. An alternative conserved cryptic site at the E protein domain interfaces showed a consistent dynamic behaviour across flaviviruses and contained a conserved cluster of ionisable residues. Constant-pH simulations revealed cluster and domain-interface disruption under low pH conditions. Based on this, we propose a cluster-dependent mechanism that addresses inconsistencies in the histidine-switch hypothesis and highlights the role of cluster protonation in orchestrating the domain dissociation pivotal for the formation of the fusogenic trimer.
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Affiliation(s)
- Lorena Zuzic
- Bioinformatics Institute (A*STAR), Singapore, Singapore
- Department of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom
| | | | - Ganesh S Anand
- Department of Biological Sciences, 16 Science Drive 4, National University of Singapore, Singapore, Singapore
- Department of Chemistry, The Pennsylvania State University, University Park, United States
| | - Jim Warwicker
- School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom
| | - Peter J Bond
- Bioinformatics Institute (A*STAR), Singapore, Singapore
- Department of Biological Sciences, 16 Science Drive 4, National University of Singapore, Singapore, Singapore
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