Postdoctoral student, University of Warsaw
My name is Monika Kowalska. I am a post-doctoral student at the Structural Biology Group, University of Warsaw, Poland, headed by Dr. Maria Górna. I am working on IFIT proteins (interferon induced proteins with tetratricopeptide repeats) which are effectors of the innate immune system. IFITs are expressed in infected cells and disrupt viral RNA by sequestration of transcripts, leading to inhibition of translation of viral proteins. The IFIT family is evolutionarily conserved in vertebrates and includes five human paralogues (IFIT1, 1B, 2, 3, 5). IFIT5 recognizes ssRNA with the triphosphate (PPP) group on the 5’end, whereas IFIT1 preferentially binds cap 0 groups on the 5’end of RNA. IFIT2 binds RNA regardless of the 5’ moiety. IFIT1 interacts with IFIT3, which is not known to bind any RNA. I am interested in the structure and function of IFIT1-IFIT3 complex. IFIT1 alone binds cap 0 RNA with nanomolar activity, but the complex IFIT1-IFIT3 binds RNA with much higher affinity (400-fold higher) than IFIT1 alone. I am trying to investigate how the two proteins interact with each other and what is the mechanism of enhanced RNA binding by the complex. To find it I am using several different methods, such as chemical crosslinking coupled with mass spectrometry, small angle x-ray scattering and microscale thermophoresis with wt and mutant IFIT1 and IFIT3. I also aim to test the activity of IFIT homologs from different organisms (fish, chicken, duck, rabbit) towards RNA binding (microscale thermophoresis, EMSA).
Abstract: Crystal structures of mouse thymidylate synthase (mTS) in complexes with (1) sulfate anion, (2) 2′-deoxyuridine 5′-monophosphate (dUMP) and (3) 5-fluoro-dUMP (FdUMP) and N5,10-methylenetetrahydrofolate (meTHF) have been determined and deposited in Protein Data Bank under the accession codes 3IHI, 4E5O and 5FCT, respectively. The structures show a strong overall similarity to the corresponding structures of rat and human thymidylate synthases (rTS and hTS, respectively). Unlike with hTS, whose unliganded and liganded forms assume different conformations (“inactive” and “active,” respectively) in the loop 181–197, in each of the three mTS structures, the loop 175–191, homologous to hTS loop 181–197, populates the active conformer, with catalytic Cys 189 buried in the active site and directed toward C(6) of the pyrimidine ring of dUMP/FdUMP, pointing to protein’s inability to adopt the inactive conformation. The binary structures of either dUMP- or sulfate-bound mTS, showing the enzyme with open active site and extended C-terminus, differ from the structure of the mTS–5-FdUMP–meTHF ternary complex, with the active site closed and C-terminus folded inward, thus covering the active site cleft. Another difference pertains to the conformation of the Arg44 side chain in the active site-flanking loop 41–47, forming strong hydrogen bonds with the dUMP/FdUMP phosphate moiety in each of the two liganded mTS structures, but turning away from the active site entrance and loosing the possibility of H-bonding with sulfate in the sulfate-bound mTS structure.
Pub.: 09 Sep '16, Pinned: 13 Jun '17
Abstract: Restriction endonuclease MvaI recognizes the sequence CC/WGG (W stands for A or T, '/' designates the cleavage site) and generates products with single nucleotide 5'-overhangs. The enzyme has been noted for its tolerance towards DNA modifications. Here, we report a biochemical characterization and crystal structures of MvaI in an apo-form and in a complex with target DNA at 1.5 A resolution. Our results show that MvaI is a monomer and recognizes its pseudosymmetric target sequence asymmetrically. The enzyme consists of two lobes. The catalytic lobe anchors the active site residues Glu36, Asp50, Glu55 and Lys57 and contacts the bases from the minor grove side. The recognition lobe mediates all major grove interactions with the bases. The enzyme in the crystal is bound to the strand with T at the center of the recognition sequence. The crystal structure with calcium ions and DNA mimics the prereactive state. MvaI shows structural similarities to BcnI, which cleaves the related sequence CC/SGG and to MutH enzyme, which is a component of the DNA repair machinery, and nicks one DNA strand instead of making a double-strand break.
Pub.: 09 Mar '07, Pinned: 13 Jun '17
Abstract: Restriction endonuclease BcnI cleaves duplex DNA containing the sequence CC/SGG (S stands for C or G, / designates a cleavage position) to generate staggered products with single nucleotide 5'-overhangs. Here, we show that BcnI functions as a monomer that interacts with its target DNA in 1:1 molar ratio and report crystal structures of BcnI in the absence and in the presence of DNA. In the complex with DNA, BcnI makes specific contacts with all five bases of the target sequence and not just with a half-site, as the protomer of a typical dimeric restriction endonuclease. Our data are inconsistent with BcnI dimerization and suggest that the enzyme introduces double-strand breaks by sequentially nicking individual DNA strands, although this remains to be confirmed by kinetic experiments. BcnI is remotely similar to the DNA repair protein MutH and shares approximately 20% sequence identity with the restriction endonuclease MvaI, which is specific for the related sequence CC/WGG (W stands for A or T). As expected, BcnI is structurally similar to MvaI and recognizes conserved bases in the target sequence similarly but not identically. BcnI has a unique machinery for the recognition of the central base-pair.
Pub.: 21 Apr '07, Pinned: 13 Jun '17
Abstract: It has long been known that most Type II restriction endonucleases share a conserved core fold and similar active-sites. The same core folding motif is also present in the MutH protein, a component of the bacterial DNA mismatch repair machinery. In contrast to most Type II restriction endonucleases, which assemble into functional dimers and catalyze double-strand breaks, MutH is a monomer and nicks hemimethylated DNA. Recent biochemical and crystallographic studies demonstrate that the restriction enzymes BcnI and MvaI share many additional features with MutH-like proteins, but not with most other restriction endonucleases. The structurally similar monomers all recognize approximately symmetric target sequences asymmetrically. Differential sensitivities to slight substrate asymmetries, which could be altered by protein engineering, determine whether the enzymes catalyze only single-strand nicks or double-strand breaks.
Pub.: 15 Jun '07, Pinned: 13 Jun '17
Abstract: The beta beta alpha-Me restriction endonuclease (REase) Hpy99I recognizes the CGWCG target sequence and cleaves it with unusual stagger (five nucleotide 5'-recessed ends). Here we present the crystal structure of the specific complex of the dimeric enzyme with DNA. The Hpy99I protomer consists of an antiparallel beta-barrel and two beta 4 alpha 2 repeats. Each repeat coordinates a structural zinc ion with four cysteine thiolates in two CXXC motifs. The beta beta alpha-Me region of the second beta 4 alpha 2 repeat holds the catalytic metal ion (or its sodium surrogate) via Asp148 and Asn165 and activates a water molecule with the general base His149. In the specific complex, Hpy99I forms a ring-like structure around the DNA that contacts DNA bases on the major and minor groove sides via the first and second beta 4 alpha 2 repeats, respectively. Hpy99I interacts with the central base pair of the recognition sequence only on the minor groove side, where A:T resembles T:A and G:C is similar to C:G. The Hpy99I-DNA co-crystal structure provides the first detailed illustration of the beta beta alpha-Me site in REases and complements structural information on the use of this active site motif in other groups of endonucleases such as homing endonucleases (e.g. I-PpoI) and Holliday junction resolvases (e.g. T4 endonuclease VII).
Pub.: 22 Apr '09, Pinned: 13 Jun '17
Abstract: The GIY-YIG nuclease domain is present in all kingdoms of life and has diverse functions. It is found in the eukaryotic flap endonuclease and Holliday junction resolvase Slx1-Slx4, the prokaryotic nucleotide excision repair proteins UvrC and Cho, and in proteins of 'selfish' genetic elements. Here we present the structures of the ternary pre- and post-cleavage complexes of the type II GIY-YIG restriction endonuclease Hpy188I with DNA and a surrogate or catalytic metal ion, respectively. Our structures suggest that GIY-YIG nucleases catalyze DNA hydrolysis by a single substitution reaction. They are consistent with a previous proposal that a tyrosine residue (which we expect to occur in its phenolate form) acts as a general base for the attacking water molecule. In contrast to the earlier proposal, our data identify the general base with the GIY and not the YIG tyrosine. A conserved glutamate residue (Glu149 provided in trans in Hpy188I) anchors a single metal cation in the active site. This metal ion contacts the phosphate proS oxygen atom and the leaving group 3'-oxygen atom, presumably to facilitate its departure. Taken together, our data reveal striking analogy in the absence of homology between GIY-YIG and ββα-Me nucleases.
Pub.: 12 Oct '10, Pinned: 13 Jun '17
Abstract: PvuRts1I is a prototype for a larger family of restriction endonucleases that cleave DNA containing 5-hydroxymethylcytosine (5hmC) or 5-glucosylhydroxymethylcytosine (5ghmC), but not 5-methylcytosine (5mC) or cytosine. Here, we report a crystal structure of the enzyme at 2.35 Å resolution. Although the protein has been crystallized in the absence of DNA, the structure is very informative. It shows that PvuRts1I consists of an N-terminal, atypical PD-(D/E)XK catalytic domain and a C-terminal SRA domain that might accommodate a flipped 5hmC or 5ghmC base. Changes to predicted catalytic residues of the PD-(D/E)XK domain or to the putative pocket for a flipped base abolish catalytic activity. Surprisingly, fluorescence changes indicative of base flipping are not observed when PvuRts1I is added to DNA substrates containing pyrrolocytosine in place of 5hmC (5ghmC). Despite this caveat, the structure suggests a model for PvuRts1I activity and presents opportunities for protein engineering to alter the enzyme properties for biotechnological applications.
Pub.: 19 Mar '14, Pinned: 13 Jun '17
Join Sparrho today to stay on top of science
Discover, organise and share research that matters to you