Ilka Müller

Georg-August-Universität Göttingen, Göttingen, Lower Saxony, Germany

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Publications (8)23.07 Total impact

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    ABSTRACT: The alkylsulfatase AtsK from Pseudomonas putida S-313 is a member of the non-heme iron(II)-alpha-ketoglutarate-dependent dioxygenase superfamily. In the initial step of their catalytic cycle, enzymes belonging to this widespread and versatile family coordinate molecular oxygen to the iron center in the active site. The subsequent decarboxylation of the cosubstrate alpha-ketoglutarate yields carbon dioxide, succinate, and a highly reactive ferryl (IV) species, which is required for substrate oxidation via a complex mechanism involving the transfer of radical species. Non-productive activation of oxygen may lead to harmful side reactions; therefore, such enzymes need an effective built-in protection mechanism. One of the ways of controlling undesired side reactions is the self-hydroxylation of an aromatic side chain, which leads to an irreversibly inactivated species. Here we describe the crystal structure of the alkylsulfatase AtsK in complexes with succinate and with Fe(II)/succinate. In the crystal structure of the AtsK-Fe(II)-succinate complex, the side chain of Tyr(168) is co-ordinated to the iron, suggesting that Tyr(168) is the target of enzyme self-hydroxylation. This is the first structural study of an Fe(II)-alpha-ketoglutarate-dependent dioxygenase that presents an aromatic side chain coordinated to the metal center, thus allowing structural insight into this protective mechanism of enzyme self-inactivation.
    Journal of Biological Chemistry 03/2005; 280(7):5716-23. · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The alkylsulfatase AtsK from Pseudomonas putida S-313 is a member of the non-heme iron(II)-α-ketoglutarate-dependent dioxygenase superfamily. In the initial step of their catalytic cycle, enzymes belonging to this widespread and versatile family coordinate molecular oxygen to the iron center in the active site. The subsequent decarboxylation of the cosubstrate α-ketoglutarate yields carbon dioxide, succinate, and a highly reactive ferryl (IV) species, which is required for substrate oxidation via a complex mechanism involving the transfer of radical species. Non-productive activation of oxygen may lead to harmful side reactions; therefore, such enzymes need an effective built-in protection mechanism. One of the ways of controlling undesired side reactions is the self-hydroxylation of an aromatic side chain, which leads to an irreversibly inactivated species. Here we describe the crystal structure of the alkylsulfatase AtsK in complexes with succinate and with Fe(II)/succinate. In the crystal structure of the AtsK-Fe(II)-succinate complex, the side chain of Tyr168 is co-ordinated to the iron, suggesting that Tyr168 is the target of enzyme self-hydroxylation. This is the first structural study of an Fe(II)-α-ketoglutarate-dependent dioxygenase that presents an aromatic side chain coordinated to the metal center, thus allowing structural insight into this protective mechanism of enzyme self-inactivation.
    Journal of Biological Chemistry 02/2005; 280(7):5716-5723. · 4.65 Impact Factor
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    ABSTRACT: The alkylsulfatase AtsK from Pseudomonas putida S-313 belongs to the widespread and versatile non-heme iron(II) alpha-ketoglutarate-dependent dioxygenase superfamily and catalyzes the oxygenolytic cleavage of a variety of different alkyl sulfate esters to the corresponding aldehyde and sulfate. The enzyme is only expressed under sulfur starvation conditions, providing a selective advantage for bacterial growth in soils and rhizosphere. Here we describe the crystal structure of AtsK in the apo form and in three complexes: with the cosubstrate alpha-ketoglutarate, with alpha-ketoglutarate and iron, and finally with alpha-ketoglutarate, iron, and an alkyl sulfate ester used as substrate in catalytic studies. The overall fold of the enzyme is closely related to that of the taurine/alpha-ketoglutarate dioxygenase TauD and is similar to the fold observed for other members of the enzyme superfamily. From comparison of these structures with the crystal structure of AtsK and its complexes, we propose a general mechanism for the catalytic cycle of the alpha-ketoglutarate-dependent dioxygenase superfamily.
    Biochemistry 04/2004; 43(11):3075-88. · 3.38 Impact Factor
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    ABSTRACT: 1-Fluordimethylsilyl-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazan reagiert mit n—BuLi zum 1-Fluordimethylsilyl-3-lithium-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazan (1). Im molaren Verhältnis 1:1 entsteht aus F2B—N(CHMe2)2 und 1 das 1-Diisopropylaminofluorboryl-3-fluordimethylsilyl- und im molaren Verhältnis 2:1 das -1, 3-Bis(diisopropylaminofluorboryl)-5-fluordimethylsilyl-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazan 2 und 3. 1, 3-Bis- und 1, 3, 5-Tris(di isopropylaminofluorboryl)-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazan 4 und 5 sind die Reaktionsprodukte aus F2BN(CHMe2)2 und di- bzw. trilithiiertem (Me2Si—NH)3. Das Dilithiumsalz des achtgliedrigen (Me2Si—NH)4 reagiert mit F2B—NR, R' (6: R, R' = CHMe2, 7: R = Me, R' = 2, 6-C6H3 (CHMe2)2) unter Erhalt des Ringgerüstes zu den 1, 5-Bis(aminofluorboryl)-2, 2, 4, 4, 6, 6, 8, 8-octamethylcyclotetrasilazanen 6 und 7. Die Kopplung von Cyclotrisilazanen und Borazinen gelingt über das lithiierte Cyclotrisilazan und (FB—NR)3 im Verhältnis 1:1 (8, 9), 2:1 (11, 12), 3:1 (13) und 1:3 (14); Me2Si(NH—SiMe2)2N—B(NR—BF)2NR (8, 9); [Me2Si(NH—SiMe2)2N]2(BNR)2BFNR (11, 12); [Me2Si(NH—SiMe2)2N]3—(BNR)3 (13); (R = Me: 8, 11, 13); (R = Et: 9, 12); (Me2Si—N)3 (B(NR—BF)2NR)3 (14). 8 reagiert mit n—BuLi unter Substitution des Fluors durch n—C4H9(10). Kinetische Ursache ist die Isomerisierung des Cyclotrisilazans zum Cyclodisilazan in der Reaktion des dilithiierten (Si—N)3-Ringes mit der bimolaren Menge (Me3CN—BF)3. Es entsteht Me3CN(BF—NCMe3)2B-NHSiMe2—(N—SiMe2)2—B(CMe3N—BF)2NCMe3 (15). Mono- und Dilithium-cyclotetrasilazane reagieren mit (FB—NEt)3 im molaren Verhältnis 1:1 und 1:2 unter Mono- und Disubstitution des Cyclotetrasilazans. Mit (Me3CN—BF)3 entsteht im molaren Verhältnis 1:2 das isomere Cyclodisilazan; [Me3CN(BF—NCMe3)2B—NHSiMe2—N—SiMe2]2 (18). Lithium-bis(trimethylsilyl) amid substituiert am (FB—NEt)3 sukzessive ein oder zwei Fluor atome; EtN(BF—NEt)2B—N(SiMe3)2 (19); FB(NEt—B)2[N(Si Me3)2]2NEt (20). 20reagiert mit (Me3Si)2NH zu Me3SiF und -Bis(3, 5-bis(bis(trimethyl)amino)-2, 4, 6-triethyl)borazinyl)amin (21); [EtN(B—N(SiMe3)2 NEt)2B]2NH. Die Kristallstrukturanalysen von 1, 3, 6, 12 — 15, 18und 21 werden diskutiert.Coupling of Cyclosilazanes with Aminofluoroboranes and Borazines1-Fluorodimethylsilyl-2, 2, 4, 4, 6, 6-hexamethylcyclotrisila zane reacts with n—BuLi to give the 1-fluorodimethylsilyl-3-lithium-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazane (1). Starting with F2B—N(CHMe2)2 and 1 1-diisopropylamino-fluoroboryl-3-fluorodimethylsilyl- and 1, 3-bis(diisopropylamino-fluoroboryl)-5-fluorodimethylsilyl-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazanes 2 und 3are formed. 1, 3-Bis- and 1, 3, 5-tris(diisopropylamino-fluoroboryl)-2, 2, 4, 4, 6, 6-hexamethylcyclotrisilazanes 4 and 5 are the products from F2BN(CHMe2)2 and di- or trilithiated (Me2Si—NH)3. The dilithium salt of the eight-membered ring (Me2Si—NH)4 reacts with F2B—NR, R' (6: R, R' = CHMe2, 7: R = Me, R' = 2, 6-C6H3 (CHMe2)2) with retention of the ring size to give 1, 5-bis(aminofluoroboryl)-2, 2, 4, 4, 6, 6, 8, 8-octamethylcyclotetrasilazanes 6 and 7. Coupling of cyclosilazanes and borazines occurs in the reaction of lithiated cyclotrisilazane and (FB—NR)3 in a molar ratio 1:1 (8, 9), 2:1 (11, 12), 3:1 (13) and 1:3 (14); Me2Si(NH—SiMe2)2N—B(NR—BF)2NR (8, 9); [Me2Si(NH—SiMe2)2N]2(BNR)2BFNR (11, 12); [Me2Si(NH—SiMe2)2N]3(BNR)3 (13); (Me2Si—N)3(B(NR—BF)2NR)3 (14); (R = Me: 8, 11, 13); (R = Et: 9, 12, 14); 8 reacts with n—BuLi under substitution of the fluorine by n—C4H9 (10). The isomerization of the cyclotri- to the cyclodisilazane in the reaction of the dilithiated (Si—N)3 ring with 2(Me3CN—BF)3 has kinetical reasons. Me3CN(BF—NCMe3)2B—NHSiMe2—(N—SiMe2)2—B(CMe3N—BF)2NCMe3 (15) is formed. Mono- and dilithiated (Me2Si—NH)4 reacts with (FB—NEt)3 in a molar ratio 1:1 and 1:2 to give the exptected mono- and disubstituted cyclotetra silazanes, the isomeric cyclodisilazane, [Me3CN(BF—NCMe3)2B—NHSiMe2—N—SiMe2]2 (18) is obtained in the reaction with (Me3CN—BF)3 in a molar ratio 1:2. Lithium-bis(trimethylsilyl)amide substitutes successively at the (FB—NEt)3 one or two fluorine atoms. EtN(BF —NEt)2B—N(SiMe3)2 (19) and FB(NEt—B)2[N(SiMe3)2]2NEt (20) are formed. 20 reacts with (Me3Si)2NH to give Me3SiF and -bis(3, 5-bis(bis(trimethylsilyl)amino-2, 4, 6-triethyl)borazinyl)amine (21); [EtN(B—N(SiMe3)2NEt)2B]2NH. The crystal structures of 1, 3, 6, 12 — 15, 18 and 21 are reported.
    Zeitschrift für anorganische Chemie 09/2002; 628:2071-2085. · 1.16 Impact Factor
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    ABSTRACT: Cetoniacytone A (1) and some related minor components (2, 6, 7) were produced by Actinomyces sp. (strain Lu 9419), which was isolated from the intestines of a rose chafer (Cetonia aureata). The structures of the novel metabolites were established by detailed spectroscopic analysis. The absolute configuration of 1 was determined by X-ray analysis and derivatisation with chiral acids. 1 exhibits a significant cytotoxicity against selected tumor cell lines. The biosynthesis of 1 was studied by feeding 13C labelled precursors. The results suggest that the characteristic p-C7N skeleton of the aminocarba sugar is formed via the pentose phosphate pathway by cyclisation of a heptulose phosphate intermediate.
    The Journal of Antibiotics 08/2002; 55(7):635-42. · 2.19 Impact Factor
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    ABSTRACT: 2,5-Bis(di-tert-butylfluorosilyl)furan reacts with potassium hydroxide in a 1:2 molar ratio to give 2,5-bis(di-tert-butylhydroxysilyl)furan, O(CRCH)2 [R = SiOH(CMe3)2 (1)]. Compound 1 is very selective in its adduct formation and forms host-guest complexes in the presence of KF [1·1/2KF (2)], H2O [1·H2O (3)], NH3 [1·NH3 (4)] and MeNH2 [1·2MeNH2 (5)]. The host-guest complexes are stable at room temperature. Compound 4 is the first neutral ammonia cage that is stable up to 100 °C. The crystal structures of 2, 3, 4 and 5 have been determined.
    Berichte der deutschen chemischen Gesellschaft 03/2002; 2002(3):717-722. · 2.94 Impact Factor
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    ABSTRACT: The reaction of the β-diketoiminate lithium complex (dipp)NacNacLi · OEt2 ((dipp)NacNac = 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-pent-2-enyl) with iPrMgCl and MgI2 yield the corresponding (dipp)NacNacMgiPr · OEt2 (1) and (dipp)NacNacMgI · OEt2 (2). The reaction of 2 with NaBH4 in diethylether gives (dipp)NacNacMg(μ-H)3BH · OEt2 (3). The core element of compounds 1–3 is a six-membered ring formed by N(1)–C(1)–C(2)–C(3)–N(2) and magnesium. The structures of 1 and 2 show the β-diketoiminate backbone in a boat-conformation with the tetrahedrally coordinated metal center at the prow and the opposing carbon atom at the stern. The magnesium atom in 3 is octahedrally coordinated and out of the β-diketoiminate plane.Synthese und Struktur von β-Diketiminato Komplexen des MagnesiumsDie Reaktion des β-Diketiminato-Lithium-Komplexes (dipp)NacNacLi · OEt2 ((dipp)NacNac = 2-((2,6Diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-pent-2-enyl) mit iPrMgCl bzw. mit MgI2 führt zur Bildung des entsprechenden (dipp)NacNacMgiPr · OEt2 (1) und (dipp)NacNacMgI · OEt2 (2). Durch Umsetzung von 2 mit NaBH4 in Diethylether wird das (dipp)NacNacMg(μ-H)3BH · OEt2 (3) erhalten. Das zentrale Strukturelement der Verbindungen 1–3 ist ein sechsgliedriger Ring bestehend aus N(1)–C(1)–C(2)–C(3)–N(2) und Magnesium. Die Strukturen von 1 und 2 stellen die β-Diketiminatoverbindungen in einer Bootkonformation dar, mit dem tetraedrisch koordinierten Metallatom auf der einen und dem gegenüberliegenden Kohlenstoffatom auf der anderen Seite. Das Magnesiumatom in 3 ist oktaedrisch koordiniert und liegt außerhalb der Ebene, die durch den β-DiketiminatoLiganden gebildet wird.
    Zeitschrift für anorganische Chemie 07/2001; 627(8):2032 - 2037. · 1.16 Impact Factor
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    ABSTRACT: We have focused on the synthesis of monomeric, functionalized starting materials containing manganese(II), zinc(II), and cadmium(II) by taking advantage of the sterically demanding and chelating property of the substituted vinamidine ligand 2-[(2,6-diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]pent-2-ene (NacNacH). Metal iodine derivatives containing vinamidines as the bulky ligand can be regarded as interesting precursors for preparing complexes with low-valent metal centers by reduction as long as they are free of coordinated ether. The vinamidine complexes NacNacM(μ-I)2Li(OEt2)2 [M = Mn (3), Zn (4), Cd (5)] are obtained from the corresponding vinamidine lithium complex and MI2 (M = Mn, Zn, Cd) in good yields. A crystal structure analysis of 3, 4, and 5 shows them to be isostructural. All three structures have the vinamidine backbone in a boat conformation with the tetrahedrally coordinated metal center at the prow and the opposing carbon atom at the stern.
    Berichte der deutschen chemischen Gesellschaft 06/2001; 2001(6):1613-1616. · 2.94 Impact Factor