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Biomedical subjects

Ole Kristensen

Publications and source records attributed to Ole Kristensen.

At least 19 recordsLinked to original sources
PubMed2006

Crystal structures of two peptide-HLA-B*1501 complexes; structural characterization of the HLA-B62 supertype.

MHC class I molecules govern human cytotoxic T cell responses. Their specificity determines which peptides they sample from the intracellular protein environment and then present to human cytotoxic T cells. More than 1100 different MHC class I proteins have been found in human populations and it would be a major undertaking to address each of these specificities individually. Based upon their peptide binding specificity, they are currently subdivided into 12 supertypes. Several of these HLA supertypes have not yet been described at the structural level. To support a comprehensive understanding of human immune responses, the structure of at least one member of each supertype should be determined. Here, the structures of two immunogenic peptide-HLA-B*1501 complexes are described. The structure of HLA-B*1501 in complex with a peptide (LEKARGSTY, corresponding to positions 274-282 in the Epstein-Barr virus nuclear antigen-3A) was determined to 2.3 A resolution. The structure of HLA-B*1501 in complex with a peptide (ILGPPGSVY) derived from human ubiquitin-conjugating enzyme-E2 corresponding to positions 91-99 was solved to 1.8 A resolution. Mutual comparisons of these two structures with structures from other HLA supertypes define and explain the specificity of the P2 and P9 peptide anchor preferences in the B62 HLA supertype. The P2 peptide residue binds to the B-pocket in HLA-B*1501. This pocket is relatively large because of the small Ser67 residue located at the bottom. The peptide proximal part of the B-pocket is hydrophobic, which is consistent with P2 anchor residue preference for Leu. The specificity of the B-pocket is determined by the Met45, Ile66 and Ser67 residues. The apex of the B-pocket is hydrophilic because of the Ser67 residue. The P9 peptide residue binds to the F-pocket in HLA-B*1501. The residues most important for the specificity of this pocket are Tyr74, Leu81, Leu95, Tyr123 and Trp147. These residues create a hydrophobic interior in the F-pocket and their spatial arrangement makes the pocket capable of containing large, bulky peptide side chains. Ser116 is located at the bottom of the F-pocket and makes the bottom of this pocket hydrophilic. Ser116, may act as a hydrogen-bonding partner and as such is a perfect place for binding of a Tyr9 peptide residue. Thus, based on structure information it is now possible to explain the peptide sequence specificity of HLA-B*1501 as previously determined by peptide binding and pool sequencing experiments.

Binding Sites↗
PubMed2006

[CADASIL versus multiple sclerosis].

This case history reports on the second family in Denmark to be diagnosed with CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy). Due to symptoms, signs and paraclinical findings, an initial diagnosis of multiple sclerosis was made. However, MRI findings of leucoencephalopathy in the external capsule and anterior temporal lobes together with negative CSF findings and family history raised suspicions of CADASIL. Skin biopsy with granular osmiophilic material (GOM) and genetic testing showing the NOTCH 3 mutation proved the diagnosis. There is considerable variability in the symptoms of CADASIL; however, most often a family history of migraine, cerebrovascular events and dementia in early life is found.

CADASIL↗
PubMed2006

Thyroid function during B-vitamin supplementation of patients on antiepileptic drugs.

OBJECTIVES: Patients on antiepileptic drugs (AEDs) may have low serum concentrations of thyroxine, with or without a compensatory increment in thyroid-stimulating hormone (TSH). Furthermore, patients on AEDs often have hyperhomocysteinemia and low concentrations of vitamins B(6), B(2) and folate. Previously, an inverse relationship between thyroxine and homocysteine concentrations has been observed. In animals, deficiency of vitamin B(6) has been found to impair the hypophyseal release of TRH. We have studied the effect of B-vitamin supplements on thyroid function in patients on AEDs. DESIGN AND METHODS: Thirty-two patients on AEDs were identified with hyperhomocysteinemia and low folate, B(6) and B(2). They were supplemented with pyridoxine, riboflavin and folic acid for 30 days. RESULTS: At baseline, the patients had low serum concentrations of free thyroxin and slightly elevated TSH. On day 30 of the B-vitamin supplements, homocysteine had decreased, however, the thyroid parameters remained unchanged. CONCLUSIONS: Hyperhomocysteinemic patients on AEDs have indications of hypothyroidism, however, supplementation with B-vitamins does not improve their thyroid function.

Adult↗
PubMed2006

A unique set of SH3-SH3 interactions controls IB1 homodimerization.

Islet-brain 1 (IB1 or JIP-1) is a scaffold protein that interacts with components of the c-Jun N-terminal kinase (JNK) signal-transduction pathway. IB1 is expressed at high levels in neurons and in pancreatic beta-cells, where it controls expression of several insulin-secretory components and secretion. IB1 has been shown to homodimerize, but neither the molecular mechanisms nor the function of dimerization have yet been characterized. Here, we show that IB1 homodimerizes through a novel and unique set of Src homology 3 (SH3)-SH3 interactions. X-ray crystallography studies show that the dimer interface covers a region usually engaged in PxxP-mediated ligand recognition, even though the IB1 SH3 domain lacks this motif. The highly stable IB1 homodimer can be significantly destabilized in vitro by three individual point mutations directed against key residues involved in dimerization. Each mutation reduces IB1-dependent basal JNK activity in 293T cells. Impaired dimerization also results in a reduction in glucose transporter type 2 expression and in glucose-dependent insulin secretion in pancreatic beta-cells. Taken together, these results indicate that IB1 homodimerization through its SH3 domain has pleiotropic effects including regulation of the insulin secretion process.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Immunomodulatory treatment of multiple sclerosis in denmark: a prospective nationwide survey.

OBJECTIVE: The aim of the present study was to provide data on the use of immunomodulatory therapies in a population comprising all treated patients with relapsing-remitting multiple sclerosis (RRMS) in Denmark. PATIENTS AND METHODS: From the introduction of immunomodulatory therapy in Denmark in 1996 through 2003, all patients that started immunomodulatory therapy were followed prospectively with neurological examination and standard laboratory tests every six months, and clinical data were reported to the MS Treatment Register, including relapses, Expanded Disability Status Scale scores and side effects. RESULTS: From 1996 through 2003 in all 2393 patients had started immunomodulatory therapy for RRMS, of whom 1252 (52.3%) were still on therapy with the same product at follow-up on 1 January 2005, whereas 1141 patients had discontinued or changed immunomodulatory therapy. Multiple Cox regression analysis of the risk of suffering a relapse showed a hazard ratio of 1.48 in patients with three or more relapses in the 24 months prior to onset compared with patients with two relapses or less; the hazard ratio was 0.84 in patients with age 238 years at treatment start compared with patients of age <38, and 1.17 for females compared with males. For disease progression the hazard ratio was 1.24 for age =38 years compared with age 2 37 years. Significant differences were observed in the hazard ratios between the different preparations, probably due to selection bias. CONCLUSION: The response to immunomodulatory therapy can be predicted to some extent from demographic variables. Differences between preparations can mainly be ascribed to selection bias, and open studies are not suited for comparison of efficacy between different preparations.

Adult↗
PubMed2005

The crystal structure of recombinant proDer p 1, a major house dust mite proteolytic allergen.

Allergy to house dust mite is among the most prevalent allergic diseases worldwide. Most house dust mite allergic patients react to Der p 1 from Dermatophagoides pteronyssinus, which is a cysteine protease. To avoid heterogeneity in the sample used for crystallization, a modified recombinant molecule was produced. The sequence of the proDer p 1 allergen was modified to reduce glycosylation and to abolish enzymatic activity. The resulting rproDer p 1 preparation was homogenous and stable and yielded crystals diffracting to a resolution of 1.61 A. The active site is located in a large cleft on the surface of the molecule. The 80-aa pro-peptide adopts a unique fold that interacts with the active site cleft and a substantial adjacent area on the mature region, excluding access to the cleft and the active site. Studies performed using crossed-line immunoelectrophoresis and IgE inhibition experiments indicated that several epitopes are covered by the pro-peptide and that the epitopes on the recombinant mature molecule are indistinguishable from those on the natural one. The structure confirms previous results suggesting a preference for aliphatic residues in the important P2 position in substrates. Sequence variations in related species are concentrated on the surface, which explains the existence of cross-reacting and species-specific antibodies. This study describes the first crystal structure of one of the clinically most important house dust mite allergens, the cysteine protease Der p 1.

Allergens↗
PubMed2005

Expression, crystallization and preliminary X-ray analysis of the extracellular Ig modules I-IV and F3 modules I-III of the neural cell-adhesion molecule L1.

Four amino-terminal immunoglobulin (Ig) modules and three fibronectin type III (F3) modules of the mouse neural cell-adhesion molecule L1 have been expressed in Drosophila S2 cells. The Ig modules I-IV of L1 crystallized in a trigonal space group, with unit-cell parameters a = b = 239.6, c = 99.3 A, and the crystals diffracted X-rays to a resolution of about 3.5 A. The F3 modules I-III of L1 crystallized in a tetragonal space group, with unit-cell parameters a = b = 80.1, c = 131 A, and the crystals diffracted X-rays to 2.8 A resolution. This is a step towards the structure determination of the multimodular constructs of the neural cell-adhesion molecule L1 in order to understand the function of L1 on a structural basis.

Animals↗
PubMed2005

Structure of the house dust mite allergen Der f 2: implications for function and molecular basis of IgE cross-reactivity.

The X-ray structure of the group 2 major allergen from Dermatophagoides farinae (Der f 2) was determined to 1.83 A resolution. The overall Der f 2 structure comprises a single domain of immunoglobulin fold with two anti-parallel beta-sheets. A large hydrophobic cavity is formed in the interior of Der f 2. Structural comparisons to distantly related proteins suggest a role in lipid binding. Immunoglobulin E (IgE) cross-reactivity between group 2 house dust mite major allergens can be explained by conserved surface areas representing IgE binding epitopes.

Allergens↗
PubMed2004

Structural characterization of the stringent response related exopolyphosphatase/guanosine pentaphosphate phosphohydrolase protein family.

Exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (PPX/GPPA) enzymes play central roles in the bacterial stringent response induced by starvation. The high-resolution crystal structure of the putative Aquifex aeolicus PPX/GPPA phosphatase from the actin-like ATPase domain superfamily has been determined, providing the first insights to features of the common catalytic core of the PPX/GPPA family. The protein has a two-domain structure with an active site located in the interdomain cleft. Two crystal forms were investigated (type I and II) at resolutions of 1.53 and 2.15 A, respectively. This revealed a structural flexibility that has previously been described as a "butterfly-like" cleft opening around the active site in other actin-like superfamily proteins. A calcium ion is observed at the center of this region in type I crystals, substantiating that PPX/GPPA enzymes use metal ions for catalysis. Structural analysis suggests that nucleotides bind at a similar position to that seen in other members of the superfamily.

Acid Anhydride Hydrolases↗
PubMed2003

Crystallization and preliminary crystallographic characterization of an SH3 domain from the IB1 scaffold protein.

IB1 is a mammalian scaffold protein that interacts with components of the c-Jun N-terminal kinase (JNK) signal-transduction pathway mainly via its protein-protein interaction domains. Crystallization of the key Src homology 3 (SH3) domain of IB1 has been achieved. Crystallization experiments with unmodified protein and deliberately oxidized protein have led to different crystal forms. X-ray data have been collected to 3.0 A resolution from a crystal form with rectangular prism morphology. These crystals are orthorhombic (P2(1)2(1)2(1)), with unit-cell parameters a = 45.9, b = 57.0, c = 145.5 A. These are the first crystallographic data on a scaffold molecule such as IB1 to be reported.

Crystallization↗
PubMed2003

Clinical importance of neutralising antibodies against interferon beta in patients with relapsing-remitting multiple sclerosis.

BACKGROUND: Interferon beta is the first-line treatment for relapsing-remitting multiple sclerosis, but the drug can induce neutralising antibodies against itself, which might reduce effectiveness. We aimed to assess the clinical effect of neutralising antibodies. METHODS: We measured neutralising antibodies every 12 months for up to 60 months in 541 patients with multiple sclerosis, randomly selected from all patients who started treatment with interferon beta between 1996 and 1999. Patients left the study if they changed or discontinued therapy. Antibodies were measured blindly, using antiviral neutralisation bioassays with high, medium, and low sensitivity, and with different neutralising capacities as cutoff value for definition of a neutralising-antibody-positive result. FINDINGS: Patients developed neutralising antibodies independent of age, sex, disease duration, and progression index at start of treatment. Relapse rates were significantly higher during antibody-positive periods (0.64-0.70) than they were during antibody-negative periods (0.43-0.46; p<0.03). When comparing the number of relapses in the neutralising-antibody-positive and neutralising-antibody-negative periods we found odds ratios in the range 1.51 to 1.58 (p<0.03). Time to first relapse was significantly increased by 244 days in patients who were antibody-negative at 12 months (log rank test 6.83, p=0.009). During this short-term study, presence of neutralising antibodies did not affect disease progression measured with the expanded disability status scale. INTERPRETATION: Our findings suggest that the presence of neutralising antibodies against interferon beta reduces the clinical effect of the drug. In patients who are not doing well on interferon beta, the presence of such antibodies should prompt consideration about change of treatment.

Adjuvants, Immunologic↗
PubMed2003

Chaperone binding at the ribosomal exit tunnel.

The exit tunnel region of the ribosome is well established as a focal point for interaction between the components that guide the fate of nascent polypeptides. One of these, the chaperone trigger factor (TF), associates with the 50S ribosomal subunit through its N-terminal domain. Targeting of TF to ribosomes is crucial to achieve its remarkable efficiency in protein folding. A similar tight coupling to translation is found in signal recognition particle (SRP)-dependent protein translocation. Here, we report crystal structures of the E. coli TF ribosome binding domain. TF is structurally related to the Hsp33 chaperone but has a prominent ribosome anchor located as a tip of the molecule. This tip includes the previously established unique TF signature motif. Comparison reveals that this feature is not found in SRP structures. We identify a conserved helical kink as a hallmark of the TF structure that is most likely critical to ensure ribosome association.

Amino Acid Motifs↗
PubMed2002

Crystallization of a stringent response factor from Aquifex aeolicus.

The crystallization of a key enzyme from Aquifex aeolicus with suggested bifunctional activity, acting as an exopolyphosphatase and a guanosine pentaphosphate phosphohydrolase, is reported. Native data were collected to below 2 A resolution from an orthorhombic crystal with unit-cell parameters a = 50.8, b = 70.3, c = 90.9 A. Methionine residues were introduced by mutation and deliberate oxidation of the protein allowed us to produce additional crystal forms with reproducible diffraction ability and increased phasing potential. This is the first report on the crystallization of a member of the Ppx/GppA phosphatase family.

Bacteria↗
PubMed2002

Expression, refolding and crystallization of Aquifex aeolicus elongation factor P.

Elongation factor P is a universally conserved protein stimulating peptidyltransferase activity during protein synthesis. The factor is sensitive to classical inhibitors of the ribosomal peptidyltransferase activity and is possibly involved in alignment of the substrate tRNAs in the catalytic centre of 70S ribosomes. Elongation factor P from the thermophilic Aquifex aeolicus was overexpressed as a soluble protein in Escherichia coli and crystallized. A fast generally applicable refolding protocol was developed to improve crystal quality and circumvent strong binding of oligonucleotides to the protein. Diffraction data collected to 2.7 A resolution present twinning.

Bacterial Proteins↗