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Instruments / Technical Area	Publication Details	Published
B21-High Throughput SAXS	Structure and mechanism of a phage-encoded SAM lyase revises catalytic function of enzyme family Xiaohu Guo , Annika Soderholm , Sandesh Kanchugal Puttaswamy , Geir V Isaksen , Omar Warsi , Ulrich Eckhard , Silvia Triguis , Adolf Gogoll , Jon Jerlström-hultqvist , Johan Åqvist , Dan I. Andersson , Maria Selmer Elife 10 DOI: 10.7554/eLife.61818 Diamond Proposal Number(s): [11171] Open Access Show Abstract ▼ Abstract: The first S-adenosyl methionine (SAM) degrading enzyme (SAMase) was discovered in bacteriophage T3, as a counter-defense against the bacterial restriction-modification system, and annotated as a SAM hydrolase forming 5’-methyl-thioadenosine (MTA) and L-homoserine. From environmental phages, we recently discovered three SAMases with barely detectable sequence similarity to T3 SAMase and without homology to proteins of known structure. Here, we present the very first phage SAMase structures, in complex with a substrate analogue and the product MTA. The structure shows a trimer of alpha–beta sandwiches similar to the GlnB-like superfamily, with active sites formed at the trimer interfaces. Quantum-mechanical calculations, thin-layer chromatography, and nuclear magnetic resonance spectroscopy demonstrate that this family of enzymes are not hydrolases but lyases forming MTA and L-homoserine lactone in a unimolecular reaction mechanism. Sequence analysis and in vitro and in vivo mutagenesis support that T3 SAMase belongs to the same structural family and utilizes the same reaction mechanism.	Feb 2021
I04-1-Macromolecular Crystallography (fixed wavelength) I04-Macromolecular Crystallography	Structural recognition of spectinomycin by resistance enzyme ANT(9) from Enterococcus faecalis Sandesh Kanchugal Puttaswamy , Maria Selmer Antimicrobial Agents And Chemotherapy DOI: 10.1128/AAC.00371-20 Diamond Proposal Number(s): [15868, 22906] Show Abstract ▼ Abstract: Spectinomycin is a ribosome-binding antibiotic that blocks the translocation step of translation. A prevalent resistance mechanism is the modification of the drug by aminoglycoside nucleotidyl transferase (ANT) enzymes of the spectinomycin-specific ANT (9) family or by the dual-specificity ANT(3") (9) family that also acts on streptomycin. We previously reported the structural mechanism of streptomycin modification by the ANT(3") (9) AadA from Salmonella enterica. ANT (9) from Enterococcus faecalis adenylates the 9-hydroxyl of spectinomycin. We here present the first structures of spectinomycin bound to an ANT enzyme. Structures were solved for ANT (9) in apo form, in complex with ATP, spectinomycin and magnesium or in complex with only spectinomycin. ANT (9) shows similar overall structure as AadA with an N-terminal nucleotidyltransferase domain and a C-terminal α-helical domain. Spectinomycin binds close to the entrance of the interdomain cleft, while ATP is buried at the bottom. Upon drug binding, the C-terminal domain rotates by 14 degrees to close the cleft, allowing contacts of both domains with the drug. Comparison with AadA shows that spectinomycin specificity is explained by a straight α5 helix and a shorter α5-α6 loop that would clash with the larger streptomycin substrate. In the active site, we observe two magnesium ions, one of them in a previously un-observed position that may activate the 9-hydroxyl for deprotonation by the catalytic base Glu-86. The observed binding mode for spectinomycin suggests that also spectinamides and aminomethyl spectinomycins, recent spectinomycin analogues with expansions in position 4 of the C ring, will be subjected to modification by ANT (9) and ANT(3") (9) enzymes.	Apr 2020
B21-High Throughput SAXS	Oligomerization and characteristics of phosphoenolpyruvate carboxylase in Synechococcus PCC 7002 Claudia Durall De La Fuente , Sandesh Kanchugal Puttaswamy , Maria Selmer , Peter Lindblad Scientific Reports 10 DOI: 10.1038/s41598-020-60249-2 Diamond Proposal Number(s): [15868] Open Access Show Abstract ▼ Abstract: Phosphoenolpyruvate carboxylase (PEPc) is an essential enzyme in plants. A photosynthetic form is present both as dimer and tetramer in C4 and CAM metabolism. Additionally, non-photosynthetic PEPcs are also present. The single, non-photosynthetic PEPc of the unicellular cyanobacterium Synechococcus PCC 7002 (Synechococcus), involved in the TC A cycle, was examined. Using size exclusion chromatography (SEC) and small angle X-ray scattering (SAXS), we observed that PEPc in Synechococcus exists as both a dimer and a tetramer. This is the first demonstration of two different oligomerization states of a non-photosynthetic PEPc. High concentration of Mg2+, the substrate PEP and a combination of low concentration of Mg2+ and HCO3 − induced the tetramer form of the carboxylase. Using SEC-SAXS analysis, we showed that the oligomerization state of the carboxylase is concentration dependent and that, among the available crystal structures of PEPc, the scattering profile of PEPc of Synechococcus agrees best with the structure of PEPc from Escherichia coli. In addition, the kinetics of the tetramer purified in presence of Mg2+ using SEC, and of the mixed population purified in presence of Mg2+ using a Strep-tagged column were examined. Moreover, the enzyme showed interesting allosteric regulation, being activated by succinate and inhibited by glutamine, and not affected by either malate, 2-oxoglutarate, aspartic acid or citric acid.	Feb 2020
I03-Macromolecular Crystallography	Structural mechanism of AadA, a dual specificity aminoglycoside adenyl transferase from Salmonella enterica Ana Laura Stern , Sander Egbert Van Der Verren , Sandesh Kanchugal Puttaswamy , Joakim Näsvall , Hugo Gutierrez De Teran , Maria Selmer Journal Of Biological Chemistry DOI: 10.1074/jbc.RA118.003989 Diamond Proposal Number(s): [11171] Show Abstract ▼ Abstract: Streptomycin and spectinomycin are antibiotics that bind to the bacterial ribosome and perturb protein synthesis. The clinically most prevalent bacterial resistance mechanism is their chemical modification by aminoglycoside-modifying enzymes such as aminoglycoside nucleotidyltransferases (ANTs). AadA from Salmonella enterica is an aminoglycoside (3’’)(9) adenylyl transferase that O-adenylates position 3” of streptomycin and position 9 of spectinomycin. We previously reported the apo AadA structure with a closed active site. To clarify how AadA binds ATP and its two chemically distinct drug substrates, we here report crystal structures of wildtype AadA complexed with ATP, magnesium, and streptomycin and of an active-site mutant, E87Q, complexed with ATP and streptomycin or the closely related dihydrostreptomycin. These structures revealed that ATP binding induces a conformational change that positions the two domains for drug binding at the interdomain cleft and disclosed the interactions between both domains and the three rings of streptomycin. Spectinomycin docking followed by molecular dynamics simulations suggested that despite the limited structural similarities with streptomycin, spectinomycin makes similar interactions around the modification site, and, in agreement with mutational data, critically interacts with fewer residues. Using structure-guided sequence analyses of ANT(3”)(9) enzymes acting on both substrates and ANT(9) enzymes active only on spectinomycin, we identified sequence determinants for activity on each substrate. We experimentally confirmed that Trp-173 and Asp-178 are essential only for streptomycin resistance. Activity assays indicated that Glu-87 is the catalytic base in AadA and that the non-adenylating E87Q mutant can hydrolyze ATP in the presence of streptomycin.	Jun 2018

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