Biomedical subjects

Mikyung Yun

Publications and source records attributed to Mikyung Yun.

8 recordsLinked to original sources

PubMed2005

Kar3 interaction with Cik1 alters motor structure and function.

Kar3, a kinesin-14 motor of Saccharomyces cerevisiae required for mitosis and karyogamy, reportedly interacts with Cik1, a nonmotor protein, via its central, predicted coiled coil. Despite this, neither Kar3 nor Cik1 homodimers have been observed in vivo. Here we show that Kar3 is a dimer in vitro by analytical ultracentrifugation. The motor domains appear as paired particles by rotary-shadow electron microscopy (EM) and circular dichroism (CD) spectroscopy of the nonmotor region shows characteristics of helical structure, typical of coiled coils. Remarkably, the Kar3/Cik1 nonmotor region shows greater helicity by CD analysis and rotary-shadow EM reveals a stalk joined to one large or two smaller particles. The highly helical Kar3/Cik1 nonmotor region and visible stalk indicate that dimerization with Cik1 causes structural changes in Kar3. The Cik1 and Kar3 stalk regions preferentially associate with one another rather than forming homodimers. Kar3/Cik1 moves on microtubules at 2-2.4 microm min(-1), 2-5-fold faster than Kar3, and destabilizes microtubules at the lagging ends. Thus, structural changes in Kar3 upon dimerization with Cik1 alter the motor velocity and likely regulate Kar3 activity in vivo.

Circular Dichroism↗

PubMed2005

Health innovation networks to help developing countries address neglected diseases.

Gross inequities in disease burden between developed and developing countries are now the subject of intense global attention. Public and private donors have marshaled resources and created organizational structures to accelerate the development of new health products and to procure and distribute drugs and vaccines for the poor. Despite these encouraging efforts directed primarily from and funded by industrialized countries, sufficiency and sustainability remain enormous challenges because of the sheer magnitude of the problem. Here we highlight a complementary and increasingly important means to improve health equity: the growing ability of some developing countries to undertake health innovation.

Biomedical Research↗

PubMed2005

Design, synthesis, and anticancer activity of fluorocyclopentenyl-pyrimidines.

Novel pyrimidine nucleosides with fluorocyclopentene ring were synthesized from D-ribose via stereoselective Grignard reaction and electrophilic vinyl fluorination as key steps. Among compounds tested, cytosine derivative 15a was found to show high growth inhibition against a broad range of human tumor cell lines.

Antineoplastic Agents↗

PubMed2004

Synthesis of 2'-azidoethyl trisaccharide, alpha-D-Gal-(1-->2)-6d-alpha-D-altro-Hepp-(1-->3)-beta-D-GlcNAc, an O-antigenic repeating unit of C. jejuni O:23 and O:36.

A trisaccharide, the O-antigenic repeating unit of C. jejuni serotype O:23 and O:36, was synthesized as a 2'-azidoethyl glycoside by block addition of perbenzylated thiogalactoside donors to alpha-altroHepp-(1-->3)-GlcNPhth disaccharide acceptor in presence of IDCP promoter. The alpha-linked altroheptopyranoside moiety in the glycosyl acceptor was effectively prepared by Swern oxidation of alpha-mannohepp-(1-->3)-GlcNPhth disaccharide followed by mild reduction with NaCNBH3.

Azides↗

PubMed2003

Rotation of the stalk/neck and one head in a new crystal structure of the kinesin motor protein, Ncd.

Molecular motors undergo conformational changes to produce force and move along cytoskeletal filaments. Structural changes have been detected in kinesin motors; however, further changes are expected because previous crystal structures are in the same or closely related conformations. We report here a 2.5 A crystal structure of the minus-end kinesin, Ncd, with the coiled-coil stalk/neck and one head rotated by approximately 75 degrees relative to the other head. The two heads are asymmetrically positioned with respect to the stalk and show asymmetry of nucleotide state: one head is fully occupied, but the other is unstably bound to ADP. Unlike previous structures, our new atomic model can be fit into cryoelectron microscopy density maps of the motor attached to microtubules, where it appears to resemble a one-head-bound motor with the stalk rotated towards the minus end. Interactions between neck and motor core residues, observed in the head that moves with the stalk, are disrupted in the other head, permitting rotation of the stalk/neck. The rotation could represent a force-producing stroke that directs the motor to the minus end.

Adenosine Diphosphate↗

PubMed2003

Crystal structures of the Dab homology domains of mouse disabled 1 and 2.

Disabled (Dab) 1 and 2 are mammalian homologues of Drosophila DAB. Dab1 is a key cytoplasmic mediator in Reelin signaling that controls cell positioning in the developing central nervous system, whereas Dab2 is an adapter protein that plays a role in endocytosis. DAB family proteins possess an amino-terminal DAB homology (DH) domain that is similar to the phosphotyrosine binding/phosphotyrosine interaction (PTB/PI) domain. We have solved the structures of the DH domains of Dab2 (Dab2-DH) and Dab1 (Dab1-DH) in three different ligand forms, ligand-free Dab2-DH, the binary complex of Dab2-DH with the Asn-Pro-X-Tyr (NPXY) peptide of amyloid precursor protein (APP), and the ternary complex of Dab1-DH with the APP peptide and inositol 1,4,5-trisphosphate (Ins-1,4,5-P3, the head group of phosphatidylinositol-4,5-diphosphate (PtdIns-4,5-P2)). The similarity of these structures suggests that the rigid Dab DH domain maintains two independent pockets for binding of the APP/lipoprotein receptors and phosphoinositides. Mutagenesis confirmed the structural determinants specific for the NPXY sequence and PtdIns-4,5-P2 binding. NMR spectroscopy confirmed that the DH domain binds to Ins-1,4,5-P3 independent of the NPXY peptides. These findings suggest that simultaneous interaction of the rigid DH domain with the NPXY sequence and PtdIns-4,5-P2 plays a role in the attachment of Dab proteins to the APP/lipoprotein receptors and phosphoinositide-rich membranes.

Adaptor Proteins, Signal Transducing↗

PubMed2003

High radiochemical yield synthesis of 3'-deoxy-3'-[18F]fluorothymidine using (5'-O-dimethoxytrityl-2'-deoxy-3'-O-nosyl-beta-D-threo pentofuranosyl)thymine and its 3-N-BOC-protected analogue as a labeling precursor.

We prepared 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) from 3'-O-nosyl thymidine derivative 3 or its pyrimidine ring N-BOC-protected analogue 5 and optimized [(18)F]fluorination condition for a high radiochemical yield. The optimal condition for [(18)F]fluorination with precursor 3 was 30 mg (41.1 micromol)/300 microl CH(3)CN at 130 degrees C for 5 min, while precursor 5 required 34 mg (40 micromol)/300 microl CH(3)CN at 110 degrees C for 5 min. After HPLC purification at neutral pH, we achieved high radiochemical yields of 40 +/- 5.2% and 42 +/- 5.4% (decay-corrected) within 60 min of preparation time with radiochemical purities of >97%.

Dideoxynucleosides↗

PubMed2001

Structure and mechanism of CTP:phosphocholine cytidylyltransferase (LicC) from Streptococcus pneumoniae.

Pneumococcal LicC is a member of the nucleoside triphosphate transferase superfamily and catalyzes the transfer of a cytidine monophosphate from CTP to phosphocholine to form CDP-choline. The structures of apo-LicC and the LicC-CDP-choline-Mg(2+) ternary complex were determined, and the comparison of these structures reveals a significant conformational change driven by the multivalent coordination of Mg(2+). The key event is breaking the Glu(216)-Arg(129) salt bridge, which triggers the coalescence of four individual beta-strands into two extended beta-sheets. These movements reorient the side chains of Trp(136) and Tyr(190) for the optimal binding and alignment of the phosphocholine moiety. Consistent with these conformational changes, LicC operates via a compulsory ordered kinetic mechanism. The structures explain the substrate specificity of LicC for CTP and phosphocholine and implicate a direct role for Mg(2+) in aligning phosphocholine for in-line nucleophilic attack and stabilizing the negative charge that develops in the pentacoordinate transition state. These results provide a structural basis for assigning a specific role for magnesium in the catalytic mechanism of pneumococcal LicC.

Catalysis↗