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Mutagenesis and homology modelling of the Tn21 integron integrase IntI1
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
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2009 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 48, no 8, 1743-1753 p.Article in journal (Refereed) Published
Abstract [en]

Horizontal DNA transfer between bacteria is widespread and a major cause of antibiotic resistance. For logistic reasons, single or combined genes are shuttled between vectors such as plasmids and   bacterial chromosomes. Special elements termed integrons operate in such shuttling and are therefore vital for horizontal gene transfer. Shorter elements carrying genes, cassettes, are integrated in the integrons, or excised from them, by virtue of a recombination site, attC, positioned in the 3' end of each unit. It is a remarkable and   possibly restricting elementary feature of attC that it must be single-stranded while the partner target site, attI, may be double-stranded. The integron integrases belong to the tyrosine recombinase family, and this work reports mutations of the integrase IntI1 from transposon Tn21, chosen within a well-conserved region characteristic of the integron integrases. The mutated proteins were  tested for binding to a bottom strand of an attC substrate, by using an electrophoresis mobility shift assay. To aid in interpreting the   results, a homology model was constructed on the basis of the crystal structure of integron integrase VchIntIA from Vibrio cholerae bound to its cognate attC substrate VCRbs. The local stability and hydrogen bonding network of key domains of the modeled structure were further examined using molecular dynamics simulations. The homology model allowed us to interpret the roles of several amino acid residues, four of which were clearly binding assay responsive upon mutagenesis. Notably, we also observed features indicating that IntI1 may be more prone to base-specific contacts with VCRbs than VchIntIA.

Place, publisher, year, edition, pages
2009. Vol. 48, no 8, 1743-1753 p.
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95309DOI: 10.1021/bi8020235ISI: 000263697300009OAI: oai:DiVA.org:uu-95309DiVA: diva2:169476
Available from: 2007-01-02 Created: 2007-01-02 Last updated: 2014-01-24Bibliographically approved
In thesis
1. Mechanisms and DNA Specificity in Site-specific Recombination of Integron Cassettes
Open this publication in new window or tab >>Mechanisms and DNA Specificity in Site-specific Recombination of Integron Cassettes
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacterial resistance to antibiotics has become a serious problem. This is due to the remarkable ability of bacteria to respond and rapidly adapt to environmental changes. Integrons are elements with the capacity for gene capture by an integron-encoded site-specific recombinase called IntI. IntI binds and acts at the recombination sites, attI and attC resulting in excision and integration of short DNA elements called gene cassettes carrying an attC site in the 3’ end. Several families of antibiotic resistance genes are borne on gene cassettes in integrons connected to mobile elements. Other cassettes reside in the larger and ancestral superintegrons located on chromosomes in both pathogenic and environmental bacteria. Due to their close connection with lateral gene transfer systems, it is possible that integrons are functionally dependent on those networks. This work presents arguments for such connections. The attC of the aadA1-qacE cassette junction in Tn21 was characterized in detail. Like other attC sites, it contains two pairs of inverted repeats and is almost palindromic. By using electrophoretic mobility shift assays, this study showed that IntI1 binds only to the bottom strand of attC. Upon folding the strand into a hairpin, a few chiral hairpin distortions define both the strand choice and also the appropriate orientation of the highly symmetrical site. Structural recognition also explains the wide sequence variation among attC sites. We have documented the initial cleavage step in recombination in IntI extracts and integrase levels in extracts were evaluated by a new method. Mutagenesis and homology modelling were performed to find amino acid residues in IntI1 that are important for recognition of attC hairpin-DNA. Comparisons were made with other tyrosine family members to explain how integron integrases differ in site-recognition and also in their mechanism of strand exchange.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 214
Keyword
Microbiology, lateral gene transfer, site-specific recombination, tyrosine recombinase, integron, single-stranded, DNA hairpin, Mikrobiologi
Research subject
Pharmaceutical Microbiology
Identifiers
urn:nbn:se:uu:diva-7429 (URN)978-91-554-6767-8 (ISBN)
Public defence
2007-01-24, C10:301, BMC, Husargatan 3, Uppsala, 09:15
Opponent
Supervisors
Available from: 2007-01-02 Created: 2007-01-02Bibliographically approved
2. Computational Modelling of Ligand Complexes with G-Protein Coupled Receptors, Ion Channels and Enzymes
Open this publication in new window or tab >>Computational Modelling of Ligand Complexes with G-Protein Coupled Receptors, Ion Channels and Enzymes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Accurate predictions of binding free energies from computer simulations are an invaluable resource for understanding biochemical processes and drug action. The primary aim of the work described in the thesis was to predict and understand ligand binding to several proteins of major pharmaceutical importance using computational methods.

We report a computational strategy to quantitatively predict the effects of alanine scanning and ligand modifications based on molecular dynamics free energy simulations. A smooth stepwise scheme for free energy perturbation calculations is derived and applied to a series of thirteen alanine mutations of the human neuropeptide Y1 G-protein coupled receptor and a series of eight analogous antagonists. The robustness and accuracy of the method enables univocal interpretation of existing mutagenesis and binding data. We show how these calculations can be used to validate structural models and demonstrate their ability to discriminate against suboptimal ones. Site-directed mutagenesis, homology modelling and docking were further used to characterize agonist binding to the human neuropeptide Y2 receptor, which is important in feeding behavior and an obesity drug target.  In a separate project, homology modelling was also used for rationalization of mutagenesis data for an integron integrase involved in antibiotic resistance.

Blockade of the hERG potassium channel by various drug-like compounds, potentially causing serious cardiac side effects, is a major problem in drug development. We have used a homology model of hERG to conduct molecular docking experiments with a series of channel blockers, followed by molecular dynamics simulations of the complexes and evaluation of binding free energies with the linear interaction energy method. The calculations are in good agreement with experimental binding affinities and allow for a rationalization of three-dimensional structure-activity relationships with implications for design of new compounds. Docking, scoring, molecular dynamics, and the linear interaction energy method were also used to predict binding modes and affinities for a large set of inhibitors to HIV-1 reverse transcriptase. Good agreement with experiment was found and the work provides a validation of the methodology as a powerful tool in structure-based drug design. It is also easily scalable for higher throughput of compounds.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1105
Keyword
computer simulations, molecular dynamics, ligand binding, free energy perturbation, linear interaction energy, binding free energy, homology modelling, structure prediction, alanine scanning, site-directed mutagenesis, hERG, GPCR, neuropeptide Y, HIV-1 reverse transcriptase, integron integrase
National Category
Theoretical Chemistry Structural Biology Biochemistry and Molecular Biology
Research subject
Molecular Biotechnology
Identifiers
urn:nbn:se:uu:diva-212103 (URN)978-91-554-8823-9 (ISBN)
Public defence
2014-01-31, B42, BMC, Husargatan 3, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-01-10 Created: 2013-12-05 Last updated: 2014-01-24

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