Lari Lehtiö

University of Oulu, Uleoborg, Oulu, Finland

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Publications (38)180.44 Total impact

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    ABSTRACT: Acetyl-CoA plays a fundamental role in cell signaling and metabolic pathways, with its cellular levels tightly controlled through reciprocal regulation of enzymes that mediate its synthesis and catabolism. ACOT12, the primary acetyl-CoA thioesterase in the liver of human, mouse, and rat, is responsible for cleavage of the thioester bond within acetyl-CoA, producing acetate and coenzyme A for a range of cellular processes. The enzyme is regulated by ADP and ATP, which is believed to be mediated through the ligand-induced oligomerization of the thioesterase domains, whereby ATP induces active dimers and tetramers, whilst apo- and ADP-bound ACOT12 are monomeric and inactive. Here, using a range of structural and biophysical techniques, it is demonstrated that ACOT12 is a trimer rather than a tetramer, and that neither ADP nor ATP exert their regulatory effects by altering the oligomeric status of the enzyme. Rather, the binding site and mechanism of ADP regulation have been determined to occur through two novel regulatory regions, one involving a large loop that links the thioesterase domains (Phe154-Thr178), defined here as RegLoop1, and a second region involving the C-terminus of thioesterase domain 2 (Gln304-Gly326), designated RegLoop2. Mutagenesis confirmed that Arg312 and Arg313 are crucial for this mode of regulation, and novel interactions with the START domain are presented together with insights into domain swapping within eukaryotic thioesterases for substrate recognition. In summary, these experiments provide the first structural insights into the regulation of this enzyme family, revealing an alternate hypothesis likely to be conserved throughout evolution.
    The Journal of biological chemistry. 07/2014;
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    ABSTRACT: Tankyrases, an enzyme subfamily of human poly(ADP-ribosyl)polymerases, are potential drug targets especially against cancer. We have evaluated inhibition of tankyrases by known PARP inhibitors and report five cocrystal structures of the most potent compounds in complex with human tankyrase 2. The inhibitors include the small general PARP inhibitors Phenanthridinone, PJ-34, and TIQ-A as well as the more advanced inhibitors EB-47 and rucaparib. The compounds anchor to the nicotinamide subsite of tankyrase 2. Crystal structures reveal flexibility of the ligand binding site with implications for drug development against tankyrases and other ADP-ribosyltransferases. EB-47 mimics the substrate NAD+ and extends from the nicotinamide to the adenosine subsite. The clinical ARTD1 inhibitor candidate rucaparib was the most potent tankyrase inhibitor identified (24 and 14 nM for tankyrases), which indicates that inhibition of tankyrases would affect the cellular responses of this compound.
    ACS Medicinal Chemistry Letters 11/2013; 5(1):18-22. · 3.31 Impact Factor
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    ABSTRACT: Human tankyrases are attractive drug targets, especially for the treatment of cancer. We identified a set of highly potent tankyrase inhibitors based on a 2-phenyl-3,4-dihydroquinazolin-4-one scaffold. Substitutions at the para position of the scaffold's phenyl group were evaluated as a strategy to increase potency and improve selectivity. The best compounds displayed single-digit nanomolar potencies, and profiling against several human diphtheria-toxin-like ADP-ribosyltransferases revealed that a subset of these compounds are highly selective tankyrase inhibitors. The compounds also effectively inhibit Wnt signaling in HEK293 cells. The binding mode of all inhibitors was studied by protein X-ray crystallography. This allowed us to establish a structural basis for the development of highly potent and selective tankyrase inhibitors based on the 2-phenyl-3,4-dihydroquinazolin-4-one scaffold and outline a rational approach to the modification of other inhibitor scaffolds that bind to the nicotinamide site of the catalytic domain.
    ChemMedChem 10/2013; · 2.84 Impact Factor
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    ABSTRACT: Tankyrases are ADP-ribosyltransferases that play key roles in various cellular pathways, including the regulation of cell proliferation, and thus, they are promising drug targets for the treatment of cancer. Flavones have been shown to inhibit tankyrases and we report here the discovery of more potent and selective flavone derivatives. Commercially available flavones with single substitutions were used for structure-activity relationship studies, and cocrystal structures of the 18 hit compounds were analyzed to explain their potency and selectivity. The most potent inhibitors were also tested in a cell-based assay, which demonstrated that they effectively antagonize Wnt signaling. To assess selectivity, they were further tested against a panel of homologous human ADP-ribosyltransferases. The most effective compound, 22 (MN-64), showed 6 nM potency against tankyrase 1, isoenzyme selectivity, and Wnt signaling inhibition. This work forms a basis for rational development of flavones as tankyrase inhibitors and guides the development of other structurally related inhibitors.
    Journal of Medicinal Chemistry 10/2013; · 5.61 Impact Factor
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    ABSTRACT: Guanine monophosphate (GMP) synthetase is a bifunctional two domain enzyme. The N-terminal glutaminase domain generates ammonia from glutamine and the C-terminal synthetase domain aminates xanthine monophosphate (XMP) to form GMP. Mammalian GMP synthetases contain a 130 residues long insert in the synthetase domain in comparison to bacterial proteins. We report here the structure of an eukaryotic GMP synthetase. Substrate XMP was bound in the crystal structure of the human GMP synthetase enzyme. XMP is bound to the synthetase domain and covered by a LID motif. The enzyme forms a dimer in the crystal structure with entirely different subunit orientations than the bacterial counterparts. The inserted sub-domain is shown to be involved in substrate binding and dimerization. Furthermore, the structural basis for XMP recognition is revealed as well as a potential allosteric site. Enzymes in the nucleotide metabolism typically display an increased activity in proliferating cells due to the increased need for nucleotides. Many drugs used as immunosuppressants and for treatment of cancer and viral diseases are indeed nucleobase- and nucleoside-based compounds, which are acting on or are activated by enzymes in this pathway. The information obtained from the crystal structure of human GMP synthetase might therefore aid in understanding interactions of nucleoside based drugs with GMP synthetase and in structure-based design of GMP synthetase specific inhibitors.
    Journal of Molecular Biology 06/2013; · 3.91 Impact Factor
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    Lari Lehtiö, Nai-Wen Chi, Stefan Krauss
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    ABSTRACT: Tankyrase 1 and tankyrase 2 are poly(ADP-ribosyl)ases that are distinguishable from other members of the enzyme family by the structural features of the catalytic domain, and the presence of a SAM multimerization domain as well as an ankyrin repeat protein-interaction domain. Tankyrases are implicated in a multitude of cellular functions including telomere homeostasis, mitotic spindle formation, vesicle transport linked to glucose metabolism, Wnt/β-catenin signaling, and viral replication. In these processes, tankyrases interact with target proteins, catalyze poly(ADP-ribosyl)ation and regulate protein interactions and stability. The proposed roles of tankyrases in disease-relevant cellular processes have made them attractive drug targets. Recently, several inhibitors have been identified. The selectivity and potency of these small molecules can be rationalized by how they fit within the NAD(+) binding groove of the catalytic domain. Some molecules bind to the nicotinamide subsite like generic ARTD inhibitors, while others bind to a distinct adenosine subsite that diverges from other ARTDs and confers specificity. A highly potent dual-site inhibitor is also available. Within the last few years, tankyrase inhibitors have proved to be useful chemical probes and potential lead compounds especially towards different specific cancers. This article is protected by copyright. All rights reserved.
    FEBS Journal 05/2013; · 4.25 Impact Factor
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    ABSTRACT: Flavonoids are known for their beneficial effects on human health and therefore the therapeutic potential of these compounds have been extensively studied. Flavone has been previously identified as a tankyrase inhibitor and to further elucidate whether tankyrases would be inhibited by other flavonoids, we performed a systematic screening of tankyrase 2 inhibitory activity using 500 natural and naturally-derived flavonoids, covering nine different flavonoid classes. All identified tankyrase inhibitors were flavones. We report crystal structures of all the hit compounds in complex with the catalytic domain of human tankyrase 2. Flavone derivatives in all 10 crystal structures bind to the nicotinamide binding site of tankyrase 2. Potencies of the active flavones towards tankyrases vary between 50 nM and 1.1 µM and flavones show up to 200-fold selectivity for tankyrases over ARTD1. The molecular details of the interactions revealed by cocrystal structures efficiently describe the properties of potent flavone derivatives inhibiting tankyrases.
    Journal of Medicinal Chemistry 04/2013; · 5.61 Impact Factor
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    ABSTRACT: Poly(ADP-ribose) polymerases (PARPs) or diphtheria toxin like ADP-ribosyl transferases (ARTDs) are enzymes that catalyze the covalent modification of proteins by attachment of ADP-ribose units to the target amino acid residues or to the growing chain of ADP-ribose. A subclass of the ARTD superfamily consists of mono-ADP-ribosyl transferases that are thought to modify themselves and other substrate proteins by covalently adding only a single ADP-ribose moiety to the target. Many of the ARTD enzymes are established or potential drug targets and a functional activity assay for them will be a valuable tool to identify selective inhibitors for each enzyme. Existing assays are not directly applicable for screening of inhibitors due to the different nature of the reaction and different target molecules. We modified and applied a fluorescence-based assay previously described for PARP1/ARTD1 and tankyrase/ARTD5 for screening of PARP10/ARTD10 and PARP15/ARTD7 inhibitors. The assay measures the amount of NAD(+) present after chemically converting it to a fluorescent analog. We demonstrate that by using an excess of a recombinant acceptor protein the performance of the activity-based assay is excellent for screening of compound libraries. The assay is homogenous and cost effective, making it possible to test relatively large compound libraries. This method can be used to screen inhibitors of mono-ARTDs and profile inhibitors of the enzyme class. The assay was optimized for ARTD10 and ARTD7, but it can be directly applied to other mono-ARTDs of the ARTD superfamily. Profiling of known ARTD inhibitors against ARTD10 and ARTD7 in a validatory screening identified the best inhibitors with submicromolar potencies. Only few of the tested ARTD inhibitors were potent, implicating that there is a need to screen new compound scaffolds. This is needed to create small molecules that could serve as biological probes and potential starting points for drug discovery projects against mono-ARTDs.
    European journal of pharmaceutical sciences: official journal of the European Federation for Pharmaceutical Sciences 02/2013; · 2.61 Impact Factor
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    ABSTRACT: Recently a novel inhibitor of Wnt signaling was discovered. The compound, WIKI4, was found to act through tankyrase inhibition and regulate β-catenin levels in many cancer cell lines and human embryonic stem cells. Here we confirm that WIKI4 is a high potency tankyrase inhibitor and that it selectively inhibits tankyrases over other ARTD enzymes tested. The binding mode of the compound to tankyrase 2 was determined by protein X-ray crystallography to 2.4 Å resolution. The structure revealed a novel binding mode to the adenosine subsite of the donor NAD(+) binding groove of the catalytic domain. Our results form a structural basis for further development of potent and selective tankyrase inhibitors based on the WIKI4 scaffold.
    PLoS ONE 01/2013; 8(6):e65404. · 3.53 Impact Factor
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    ABSTRACT: Tankyrase, a member of human PARP protein superfamily, catalyzes a covalent post-translational modification of substrate proteins. This modification, poly(ADP-ribos)ylation, leads to changes in protein interactions and modifies downstream signaling events. Tankyrase 1 is a potential drug target due to its functions in telomere homeostasis and in Wnt signaling. We describe here optimization and application of an activity-based homogenous assay for tankyrase inhibitors in a high-throughput screening format. The method measures the consumption of substrate by the chemical conversion of the remaining NAD(+) into a stable fluorescent condensation product. Conditions were optimized to measure the enzymatic auto-modification of a recombinant catalytic fragment of tankyrase 1. The fluorescence assay is inexpensive, operationally easy and performs well according to the statistical analysis (Z'= 0.7). A validatory screen with a natural product library confirmed suitability of the assay for finding new tankyrase inhibitors. Flavone was the most potent (IC(50)=325 nM) hit from the natural compounds. A flavone derivative, apigenin, and isopropyl gallate showed potency on the micromolar range, but displayed over 30-fold selectivity for tankyrase over the studied isoenzymes PARP1 and PARP2. The assay is robust and will be useful for screening new tankyrase inhibitors.
    Journal of Biomolecular Screening 02/2012; 17(5):593-604. · 2.21 Impact Factor
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    ABSTRACT: Tankyrases are poly(ADP-ribose) polymerases that have many cellular functions. They play pharmaceutically important roles, at least in telomere homeostasis and Wnt signaling, by covalently ADP-ribosylating target proteins and consequently regulating their functions. These features make tankyrases potential targets for treatment of cancer. We report here crystal structures of human tankyrase 2 catalytic fragment in complex with a byproduct, nicotinamide, and with selective inhibitors of tankyrases (IWR-1) and PARPs 1 and 2 (olaparib). Binding of these inhibitors to tankyrase 2 induces specific conformational changes. The crystal structures explain the selectivity of the inhibitors, reveal the flexibility of a substrate binding loop, and explain existing structure-activity relationship data. The first crystal structure of a PARP enzyme in complex with a potent inhibitor, IWR-1, that does not bind to the widely utilized nicotinamide-binding site makes the structure valuable for development of PARP inhibitors in general.
    Journal of Medicinal Chemistry 02/2012; 55(3):1360-7. · 5.61 Impact Factor
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    ABSTRACT: Poly(ADP-ribosylation) is a post-translational covalent modification of proteins catalyzed by a family of enzymes termed poly(ADP-ribose) polymerases (PARPs). In the human genome, 17 different genes have been identified that encode members of the PARP superfamily. Poly (ADP-ribose) metabolism plays a role in a wide range of biological processes. In Trypanosoma cruzi, PARP enzyme appears to play a role in DNA repair mechanisms and may also be involved in controlling the different phases of cell growth. Here we describe the identification of potent inhibitors for T. cruzi PARP with a fluorescence-based activity assay. The inhibitors were also tested on T. cruzi epimastigotes, showing that they reduced ADP-ribose polymer formation in vivo. Notably, the identified inhibitors are able to reduce the growth rate of T. cruzi epimastigotes. The best inhibitor, Olaparib, is effective at nanomolar concentrations, making it an efficient chemical tool for chacterization of ADP-ribose metabolism in T. cruzi. PARP inhibition also decreases drastically the amount of amastigotes but interestingly has no effect on the amount of trypomastigotes in the cell culture. Knocking down human PARP-1 decreases both the amount of amastigotes and trypomastigotes in cell culture, indicating that the effect would be mainly due to inhibition of human PARP-1. The result suggests that the inhibition of PARP could be a potential way to interfere with T. cruzi infection.
    PLoS ONE 01/2012; 7(9):e46063. · 3.53 Impact Factor
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    ABSTRACT: Steroidogenic acute regulatory (StAR) protein related lipid transfer (START) domains are small globular modules that form a cavity where lipids and lipid hormones bind. These domains can transport ligands to facilitate lipid exchange between biological membranes, and they have been postulated to modulate the activity of other domains of the protein in response to ligand binding. More than a dozen human genes encode START domains, and several of them are implicated in a disease. We report crystal structures of the human STARD1, STARD5, STARD13 and STARD14 lipid transfer domains. These represent four of the six functional classes of START domains. Sequence alignments based on these and previously reported crystal structures define the structural determinants of human START domains, both those related to structural framework and those involved in ligand specificity. This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.
    PLoS ONE 01/2011; 6(6):e19521. · 3.53 Impact Factor
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    ABSTRACT: Human purine de novo synthesis pathway contains several multi-functional enzymes, one of which, tri-functional GART, contains three enzymatic activities in a single polypeptide chain. We have solved structures of two domains bearing separate catalytic functions: glycinamide ribonucleotide synthetase and aminoimidazole ribonucleotide synthetase. Structures are compared with those of homologous enzymes from prokaryotes and analyzed in terms of the catalytic mechanism. We also report small angle X-ray scattering models for the full-length protein. These models are consistent with the enzyme forming a dimer through the middle domain. The protein has an approximate seesaw geometry where terminal enzyme units display high mobility owing to flexible linker segments. This resilient seesaw shape may facilitate internal substrate/product transfer or forwarding to other enzymes in the pathway.
    Nucleic Acids Research 11/2010; 38(20):7308-19. · 8.81 Impact Factor
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    ABSTRACT: The early B-cell factor (EBF) transcription factors are central regulators of development in several organs and tissues. This protein family shows low sequence similarity to other protein families, which is why structural information for the functional domains of these proteins is crucial to understand their biochemical features. We have used a modular approach to determine the crystal structures of the structured domains in the EBF family. The DNA binding domain reveals a striking resemblance to the DNA binding domains of the Rel homology superfamily of transcription factors but contains a unique zinc binding structure, termed zinc knuckle. Further the EBF proteins contain an IPT/TIG domain and an atypical helix-loop-helix domain with a novel type of dimerization motif. The data presented here provide insights into unique structural features of the EBF proteins and open possibilities for detailed molecular investigations of this important transcription factor family.
    Journal of Biological Chemistry 08/2010; 285(34):25875-9. · 4.65 Impact Factor
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    ABSTRACT: The PARP-3 protein is closely related to the PARP-1 and PARP-2 proteins, which are involved in DNA repair and genome maintenance. Here, we characterized the biochemical properties of human PARP-3. PARP-3 is able to ADP-ribosylate itself as well as histone H1, a previously unknown substrate for PARP-3. PARP-3 is not activated upon binding to DNA and is a mono-ADP-ribosylase, in contrast to PARP-1 and PARP-2. PARP-3 interacts with PARP-1 and activates PARP-1 in the absence of DNA, resulting in synthesis of polymers of ADP-ribose. The N-terminal WGR domain of PARP-3 is involved in this activation. The functional interaction between PARP-3 and PARP-1 suggests that it may have a role in DNA repair. However, here we report that PARP-3 small interfering RNA-depleted cells are not sensitive to the topoisomerase I poison camptothecin, inducing DNA single-strand breaks, and repair these lesions as efficiently as wild-type cells. Altogether, these results suggest that the interaction between PARP-1 and PARP-3 is unrelated to DNA single-strand break repair.
    Journal of Biological Chemistry 03/2010; 285(11):8054-60. · 4.65 Impact Factor
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    ABSTRACT: Nucleotide-binding cystathionine beta-synthase (CBS) domains serve as regulatory units in numerous proteins distributed in all kingdoms of life. However, the underlying regulatory mechanisms remain to be established. Recently, we described a subfamily of CBS domain-containing pyrophosphatases (PPases) within family II PPases. Here, we express a novel CBS-PPase from Clostridium perfringens (CPE2055) and show that the enzyme is inhibited by AMP and activated by a novel effector, diadenosine 5',5-P1,P4-tetraphosphate (AP(4)A). The structures of the AMP and AP(4)A complexes of the regulatory region of C. perfringens PPase (cpCBS), comprising a pair of CBS domains interlinked by a DRTGG domain, were determined at 2.3 A resolution using X-ray crystallography. The structures obtained are the first structures of a DRTGG domain as part of a larger protein structure. The AMP complex contains two AMP molecules per cpCBS dimer, each bound to a single monomer, whereas in the activator-bound complex, one AP(4)A molecule bridges two monomers. In the nucleotide-bound structures, activator binding induces significant opening of the CBS domain interface, compared with the inhibitor complex. These results provide structural insight into the mechanism of CBS-PPase regulation by nucleotides.
    Journal of Molecular Biology 03/2010; 398(3):400-13. · 3.91 Impact Factor
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    ABSTRACT: The 70-kDa heat shock proteins (Hsp70) are chaperones with central roles in processes that involve polypeptide remodeling events. Hsp70 proteins consist of two major functional domains: an N-terminal nucleotide binding domain (NBD) with ATPase activity, and a C-terminal substrate binding domain (SBD). We present the first crystal structures of four human Hsp70 isoforms, those of the NBDs of HSPA1L, HSPA2, HSPA5 and HSPA6. As previously with Hsp70 family members, all four proteins crystallized in a closed cleft conformation, although a slight cleft opening through rotation of subdomain IIB was observed for the HSPA5-ADP complex. The structures presented here support the view that the NBDs of human Hsp70 function by conserved mechanisms and contribute little to isoform specificity, which instead is brought about by the SBDs and by accessory proteins. ENHANCED VERSION: This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.
    PLoS ONE 01/2010; 5(1):e8625. · 3.53 Impact Factor
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    ABSTRACT: DEAD-box RNA helicases play various, often critical, roles in all processes where RNAs are involved. Members of this family of proteins are linked to human disease, including cancer and viral infections. DEAD-box proteins contain two conserved domains that both contribute to RNA and ATP binding. Despite recent advances the molecular details of how these enzymes convert chemical energy into RNA remodeling is unknown. We present crystal structures of the isolated DEAD-domains of human DDX2A/eIF4A1, DDX2B/eIF4A2, DDX5, DDX10/DBP4, DDX18/myc-regulated DEAD-box protein, DDX20, DDX47, DDX52/ROK1, and DDX53/CAGE, and of the helicase domains of DDX25 and DDX41. Together with prior knowledge this enables a family-wide comparative structural analysis. We propose a general mechanism for opening of the RNA binding site. This analysis also provides insights into the diversity of DExD/H- proteins, with implications for understanding the functions of individual family members.
    PLoS ONE 01/2010; 5(9). · 3.53 Impact Factor
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    ABSTRACT: The human SnoN is an oncoprotein that interacts with several transcription-regulatory proteins such as the histone-deacetylase, N-CoR containing co-repressor complex and Smad proteins. This study presents the crystal structure of the Dachshund homology domain of human SnoN. The structure reveals a groove composed of conserved residues with characteristic properties of a protein-interaction surface. A comparison of the 12 monomers in the asymmetric unit reveals the presence of two major conformations: an open conformation with a well accessible groove and a tight conformation with a less accessible groove. The variability in the backbone between the open and the tight conformations matches the differences seen in previously determined structures of individual Dachshund homology domains, suggesting a general plasticity within this fold family. The flexibility observed in the putative protein binding groove may enable SnoN to recognize multiple interaction partners. ENHANCED VERSION: This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.
    PLoS ONE 01/2010; 5(9):e12907. · 3.53 Impact Factor

Publication Stats

487 Citations
180.44 Total Impact Points

Institutions

  • 2012–2014
    • University of Oulu
      • Department of Biochemistry
      Uleoborg, Oulu, Finland
    • University of Buenos Aires
      • Institute of Genetic Engineering and Molecular Biology
      Buenos Aires, Buenos Aires F.D., Argentina
  • 2013
    • Biocenter Finland
      Helsinki, Southern Finland Province, Finland
  • 2010–2012
    • Åbo Akademi University
      • Department of Biosciences
      Turku, Western Finland, Finland
  • 2008–2010
    • Karolinska Institutet
      • Institutionen för medicinsk biokemi och biofysik
      Solna, Stockholm, Sweden
  • 2006
    • Universität Stuttgart
      • Institute of Organic Chemistry
      Stuttgart, Baden-Württemberg, Germany
  • 2003–2006
    • University of Helsinki
      • Institute of Biotechnology
      Helsinki, Province of Southern Finland, Finland