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Crystal structures of OrfX2 and P47 from a Botulinum neurotoxin OrfX-type gene cluster
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.ORCID iD: 0000-0002-4854-5531
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Umeå University, Sweden.ORCID iD: 0000-0001-6848-322x
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2017 (English)In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 591, no 22, p. 3781-3792Article in journal (Refereed) Published
Abstract [en]

Botulinum neurotoxins are highly toxic substances and are all encoded together with one of two alternative gene clusters, the HA or the OrfX gene cluster. Very little is known about the function and structure of the proteins encoded in the OrfX gene cluster, which in addition to the toxin contains five proteins (OrfX1, OrfX2, OrfX3, P47, and NTNH). We here present the structures of OrfX2 and P47, solved to 2.1 and 1.8 Å, respectively. We show that they belong to the TULIP protein superfamily, which are often involved in lipid binding. OrfX1 and OrfX2 were both found to bind phosphatidylinositol lipids.

Place, publisher, year, edition, pages
2017. Vol. 591, no 22, p. 3781-3792
Keywords [en]
botulinum neurotoxin, Crystallography, gene cluster, TULIP, X-ray
National Category
Structural Biology Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-150675DOI: 10.1002/1873-3468.12889ISI: 000416726600008OAI: oai:DiVA.org:su-150675DiVA, id: diva2:1170198
Funder
Swedish Research Council, 2014-5667Wenner-Gren FoundationsSwedish Cancer SocietyAvailable from: 2018-01-02 Created: 2018-01-02 Last updated: 2022-02-28Bibliographically approved
In thesis
1. Structural and functional studies of proteins of medical relevance: Protein-ligand complexes in cancer and novel structural folds in bacteria
Open this publication in new window or tab >>Structural and functional studies of proteins of medical relevance: Protein-ligand complexes in cancer and novel structural folds in bacteria
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray crystallography is a tool for determining the structures of proteins and protein-ligand complexes. In this thesis the method has been employed to study several proteins of medical relevance.

Cancer is a terrible disease, severely impacting those affected, as well as their family and friends. Current cancer treatments involve a combination of cytostatic drugs, surgery and radiation treatment. Unfortunately many cytostatic drugs also kill healthy cells, which gives rise to serious side-effects. The discovery of treatments which selectively inhibit proteins essential for cancer cell survival but which are non-essential in normal cells, could reduce such side-effects.

MTH1 is a protein that degrades oxidised nucleotides, which when incorporated into DNA cause mutations and subsequent cell death. Cancer cells have higher levels of reactive oxygen species, which create oxidised nucleotides.  In Paper I it was discovered that cancer cells are dependent on MTH1 for their survival. Crystal structures of MTH1 in complex with small molecules guided their development into potent MTH1 inhibitors, capable of killing cancer cells. Cells with increased amounts of oxidised nucleotides, or with induced hypoxia, were more susceptible to MTH1 inhibition, as shown in Paper II. In Paper III several MTH1 orthologues from organisms often used in pre-clinical studies were tested for MTH1 inhibition. Leucine 116 of mouse MTH1 was determined to be important for the lower inhibition of the developed inhibitors towards this enzyme. A virtual fragment screening study using commercial chemicals resulted in several potent MTH1 inhibitors, as shown in Paper IV. The crystal structures with the fragments or optimised inhibitors did in most cases agree with the docking pose determined from the virtual screening. In addition to the known function of MTH1 in the degradation of oxidised nucleotides, Paper V showed that MTH1 also degrades methylated nucleotides.

MTHFD2 is responsible for providing one-carbon units for nucleotide synthesis in cancer cells. As MTHFD2 is present in cancer cells but not in healthy cells, targeting the enzyme would make it possible to selectively kill cancer cells. Paper VI presents the first structure of MTHFD2, along with the first inhibitor of the protein. This information provides a starting point for the development of potent and selective MTHFD2 inhibitors.

The botulinum neurotoxin from the bacterium Clostridium Botulinum is the causative agent of the deadly disease botulism. The action of the botulinum neurotoxin on nerve cells results in paralysis, and is life-threatening if the patient is not helped with breathing support. However, low doses of the neurotoxin are used as a successful treatment for several medical conditions, such as involuntary spasms. In Paper VII the structure of two proteins, P47 and OrfX2, encoded in the gene cluster of a botulinum neurotoxin, were determined. The structures resembled tubular lipid-binding proteins, previously only found in eukaryotes. The proteins were also found to be able to bind lipids. This work gives new insight into the structure and function of this group of proteins, which help the deadly botulinum neurotoxins.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2018. p. 79
Keywords
X-ray crystallography, Cancer, MTH1, oxidised nucleotides, MTHFD2, nucleotide metabolism, one-carbon metabolism, Botulism, Botulinum neurotoxin, OrfX, OrfX gene cluster
National Category
Biochemistry and Molecular Biology Structural Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-150688 (URN)978-91-7797-097-2 (ISBN)978-91-7797-098-9 (ISBN)
Public defence
2018-02-16, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

Available from: 2018-01-24 Created: 2018-01-02 Last updated: 2022-02-28Bibliographically approved
2. Structural Insights into Botulinum Neurotoxins and the ALFA-tag System: Structural and Functional Studies of Proteins Related to the Botulinum Neurotoxins and Design of a Novel Epitope Tag
Open this publication in new window or tab >>Structural Insights into Botulinum Neurotoxins and the ALFA-tag System: Structural and Functional Studies of Proteins Related to the Botulinum Neurotoxins and Design of a Novel Epitope Tag
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is divided into two sections; the first part describes our work in the field of botulinum neurotoxins (presented in papers I, II, III, and manuscript IV) and the second part summarizes our work involving the design of a new biochemical tool (presented in paper V).

Botulinum neurotoxins (BoNTs) produced by the anaerobic bacterium Clostridium botulinum are the most poisonous substances known to date. They have a conserved structure that consists of three domains (receptor-binding, translocation, and catalytic domain), each of which has a distinct function. The receptor-binding domain binds to neuronal receptors, and after endocytosis the translocation domain shuttles the catalytic domain into the cytosol, where it cleaves neuronal proteins of the SNARE family, which are part of the vesicle-membrane fusion machinery.

In paper I, we studied proteins of unknown function (OrfX1, OrfX2, OrfX3, and P47), which are co-expressed with certain BoNTs. We solved the crystal structures of OrfX2 and P47, and their structural resemblance to tubular lipid binding proteins (TULIP) together with lipid binding studies, led us to conclude that OrfX1 and P47 are able to bind phosphatidyl inositol phosphates (PIPs) in vitro.

In paper II, we studied the binding of BoNT/B, /DC and /G to their protein receptor synaptotagmin (Syt). We determined their affinities to synaptotagmins from different species, and concluded that residue F50 in bovine Syt-II is responsible for its increased affinity towards BoNT/DC. In addition, we studied the interaction between BoNT/G and Syt-II via STD-NMR. Our results showed the binding to be similar to BoNT/B and Syt-II, and that the N-terminal region of the Syt peptide is important for the binding of BoNTs to synaptotagmin, even though it is not part of the binding interface.

In paper III and manuscript IV, we present the identification of a novel BoNT serotype named BoNT/X. We showed that BoNT/X cleaves the non-canonical substrates VAMP4, VAMP5 and Ykt6, as well as the canonical substrate VAMP1-3 at a new cleavage site, distinct from other BoNTs. In addition, we present the cryo-EM structure of BoNT/X in complex with its non-toxic interaction partner NTNH. Our pH stability experiments revealed that BoNT/X-NTNH remain bound at neutral to moderately high pH, in contrast with what is observed for BoNT/A-NTNH.

In paper V we present the design of a novel epitope tag named the ALFA system. The ALFA tag is a short α-helical protein tag that is highly stable and electroneutral. The ALFA nanobody has a very high affinity for the tag and is small enough to allow for high performance in high-resolution microscopy. The crystal structure of the ALFA nanobody in complex with the tag led to a modified version of the ALFA nanobody that can release the tag via competitive elution with free ALFA peptide. Our results showed that this system outperforms several commercially available systems in protein purification and high-resolution microscopy.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2020. p. 60
Keywords
botulinum neurotoxin
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-178474 (URN)978-91-7911-002-4 (ISBN)978-91-7911-003-1 (ISBN)
Public defence
2020-03-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2020-02-19 Created: 2020-01-29 Last updated: 2022-02-26Bibliographically approved

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Gustafsson, RobertBerntsson, Ronnie P. A.Martínez-Carranza, MarkelOdegrip, RichardStenmark, Pål

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