Biomedical subjects

Kyou-Hoon Han

Publications and source records attributed to Kyou-Hoon Han.

12 recordsLinked to original sources

PubMed2006

Solution structure and membrane interaction mode of an antimicrobial peptide gaegurin 4.

We have applied NMR spectroscopy to determine the high-resolution structure of gaegurin 4, a 37-residue antimicrobial peptide from Rana rugosa, under varying hydrophobic conditions. Even in 100% H2O, gaegurin 4 contains a nascent turn near its C-terminal Rana box. Under a more hydrophobic condition it forms two amphipathic helices, one long encompassing residues 2-23 and the other consisting of residues 25-34, similar to what has been observed in cecropin A. Functional implication of the helix-breaking kink at Gly24 in gaegurin 4 was investigated by preparing several analogs. Based upon the current and previous results, we propose a novel seaanemone-like ion pore-forming model for gaegurin 4.

Amino Acid Sequence↗

PubMed2006

NMR structure determination of alpha-conotoxin BuIA, a novel neuronal nicotinic acetylcholine receptor antagonist with an unusual 4/4 disulfide scaffold.

We have determined a high-resolution three-dimensional structure of alpha-conotoxin BuIA, a 13-residue peptide toxin isolated from Conus bullatus. Despite its unusual 4/4 disulfide bond layout alpha-conotoxin BuIA exhibits strong antagonistic activity at alpha6/alpha3beta2beta3, alpha3beta2, and alpha3beta4 nAChR subtypes like some alpha4/7 conotoxins. alpha-Conotoxin BuIA lacks the C-terminal beta-turn present within the second disulfide loop of alpha4/7 conotoxins, having only a "pseudo omega-shaped" molecular topology. Nevertheless, it contains a functionally critical two-turn helix motif, a feature ubiquitously found in alpha4/7 conotoxins. Such an aspect seems mainly responsible for similarities in the receptor recognition profile of alpha-conotoxin BuIA to alpha4/7 conotoxins. Structural comparison of alpha-conotoxin BuIA with alpha4/7 conotoxins and alpha4/3 conotoxin ImI suggests that presence of the second helical turn portion of the two-turn helix motif in alpha4/7 and alpha4/4 conotoxins may be important for binding to the alpha3 and/or alpha6 subunit of nAChR.

Animals↗

PubMed2006

Solution conformation of an immunodominant epitope in the hepatitis B virus preS2 surface antigen.

We have determined the solution conformation of the major B cell epitope (residues 123-145, adrl23 hereafter) in the preS2 region of hepatitis B virus known to be associated with infection neutralization. The adrl23 shows an "L" shaped helix-turn-helix topology with two beta-turns formed by residues Ala(130)-Asp(133) and Asp(133)-Val(136) intervening the N- and C-terminal helices. The N-terminal alpha-helix consists of residues Ser(124)-Gln(129) whereas the C-terminal 3(10) helix is formed by residues Val(136)-Tyr(140). The beta-turns overlap partially with the putative "conformational" epitope. The overall topology of adrl23 is primarily maintained by hydrophobic interactions involving Phe(127), Leu(131), Leu(132), Val(136), and Tyr(140) that are clustered on one side of the molecule. An additional hydrophobic stabilization comes from Phe(141) that is buried inside the concave side of the molecule. A network of hydrogen bonds formed among Thr(125), His(128), and Arg(137) further contribute to the "boomerang-shaped" architecture of adrl23. The N-terminus of adrl23 is immobile due to a hydrogen bond between the N-terminal amide proton of Asn(123) and the hydroxyl oxygen of Thr(126). The side chains of Asp(133), Arg(135), Val(136), Leu(139), and Tyr(140) that were shown to be important for binding to a monoclonal antibody H8 mAb are surface exposed.

Helix-Turn-Helix Motifs↗

PubMed2006

Alpha-conotoxin OmIA is a potent ligand for the acetylcholine-binding protein as well as alpha3beta2 and alpha7 nicotinic acetylcholine receptors.

The molluskan acetylcholine-binding protein (AChBP) is a homolog of the extracellular binding domain of the pentameric ligand-gated ion channel family. AChBP most closely resembles the alpha-subunit of nicotinic acetylcholine receptors and in particular the homomeric alpha7 nicotinic receptor. We report the isolation and characterization of an alpha-conotoxin that has the highest known affinity for the Lymnaea AChBP and also potently blocks the alpha7 nAChR subtype when expressed in Xenopus oocytes. Remarkably, the peptide also has high affinity for the alpha3beta2 nAChR indicating that alpha-conotoxin OmIA in combination with the AChBP may serve as a model system for understanding the binding determinants of alpha3beta2 nAChRs. alpha-Conotoxin OmIA was purified from the venom of Conus omaria. It is a 17-amino-acid, two-disulfide bridge peptide. The ligand is the first alpha-conotoxin with higher affinity for the closely related receptor subtypes, alpha3beta2 versus alpha6beta2, and selectively blocks these two subtypes when compared with alpha2beta2, alpha4beta2, and alpha1beta1deltaepsilon nAChRs.

Amino Acid Sequence↗

PubMed2006

A helix-induced oligomeric transition of gaegurin 4, an antimicrobial peptide isolated from a Korean frog.

Gaegurin 4 (GGN4), a novel peptide isolated from the skin of a Korean frog, Rana rugosa, has broad spectrum antimicrobial activity. A number of amphipathic peptides closely related to GGN4 undergo a coil to helix transition with concomitant oligomerization in lipid membranes or membrane-mimicking environments. Despite intensive study of their secondary structures, the oligomeric states of the peptides before and after the transition are not well understood. To clarify the structural basis of its antibiotic action, we used analytical ultracentrifugation to define the aggregation state of GGN4 in water, ethyl alcohol, and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The maximum size of GGN4 in 15% HFIP corresponded to a decamer, whereas it was monomeric in buffer. The oligomeric transition is accompanied by a cooperative 9 nm blue-shift of maximum fluorescence emission and a large secondary structure change from an almost random coil to an alpha-helical structure. GGN4 induces pores in lipid membranes and, using electrophysiological methods, we estimated the diameter of the pores to be exceed 7.3 A, which suggests that the minimal oligomer structure responsible is a pentamer.

Animals↗

PubMed2006

Solution conformation of a neuronal nicotinic acetylcholine receptor antagonist alpha-conotoxin OmIA that discriminates alpha3 vs. alpha6 nAChR subtypes.

alpha-Conotoxin OmIA from Conus omaria is the only alpha-conotoxin that shows a approximately 20-fold higher affinity to the alpha3beta2 over the alpha6beta2 subtype of nicotinic acetylcholine receptor. We have determined a three-dimensional structure of alpha-conotoxin OmIA by nuclear magnetic resonance spectroscopy. alpha-Conotoxin OmIA has an "omega-shaped" overall topology with His(5)-Asn(12) forming an alpha-helix. Structural features of alpha-conotoxin OmIA responsible for its selectivity are suggested by comparing its surface characteristics with other functionally related alpha4/7 subfamily conotoxins. Reduced size of the hydrophilic area in alpha-conotoxin OmIA seems to be associated with the reduced affinity towards the alpha6beta2 nAChR subtype.

Binding Sites↗

PubMed2005

Solution structure of alpha-conotoxin PIA, a novel antagonist of alpha6 subunit containing nicotinic acetylcholine receptors.

alpha-Conotoxin PIA is a novel nicotinic acetylcholine receptor (nAChR) antagonist isolated from Conus purpurascens that targets nAChR subtypes containing alpha6 and alpha3 subunits. alpha-conotoxin PIA displays 75-fold higher affinity for rat alpha6/alpha3beta2beta3 nAChRs than for rat alpha3beta2 nAChRs. We have determined the three-dimensional structure of alpha-conotoxin PIA by nuclear magnetic resonance spectroscopy. The alpha-conotoxin PIA has an "omega-shaped" overall topology as other alpha4/7 subfamily conotoxins. Yet, unlike other neuronally targeted alpha4/7-conotoxins, its N-terminal tail Arg1-Asp2-Pro3 protrudes out of its main molecular body because Asp2-Pro3-Cys4-Cys5 forms a stable type I beta-turn. In addition, a kink introduced by Pro15 in the second loop of this toxin provides a distinct steric and electrostatic environment from those in alpha-conotoxins MII and GIC. By comparing the structure of alpha-conotoxin PIA with other functionally related alpha-conotoxins we suggest structural features in alpha-conotoxin PIA that may be associated with its unique receptor recognition profile.

Amino Acid Sequence↗

PubMed2005

Structural details on mdm2-p53 interaction.

Mdm2 is a cellular antagonist of p53 that keeps a balanced cellular level of p53. The two proteins are linked by a negative regulatory feedback loop and physically bind to each other via a putative helix formed by residues 18-26 of p53 transactivation domain (TAD) and its binding pocket located within the N-terminal 100-residue domain of mdm2 (Kussie, P. H., Gorina, S., Marechal, V., Elenbaas, B., Moreau, J., Levine, A. J., and Pavletich, N. P. (1996) Science 274, 948-953). In a previous report we demonstrated that p53 TAD in the mdm2-freee state is mostly unstructured but contains two nascent turns in addition to a "preformed" helix that is the same as the putative helix mediating p53-mdm2 binding. Here, using heteronuclear multidimensional NMR methods, we show that the two nascent turn motifs in p53 TAD, turn I (residues 40-45) and turn II (residues 49-54), are also capable of binding to mdm2. In particular, the turn II motif has a higher mdm2 binding affinity ( approximately 20 mum) than the turn I and targets the same site in mdm2 as the helix. Upon mdm2 binding this motif becomes a well defined full helix turn whose hydrophobic face formed by the side chains of Ile-50, Trp-53, and Phe-54 inserts deeply into the helix binding pocket. Our results suggest that p53-mdm2 binding is subtler than previously thought and involves global contacts such as multiple "non-contiguous" minimally structured motifs instead of being localized to one small helix mini-domain in p53 TAD.

Amino Acid Motifs↗

PubMed2004

Solution conformation of alpha-conotoxin GIC, a novel potent antagonist of alpha3beta2 nicotinic acetylcholine receptors.

Alpha-conotoxin GIC is a 16-residue peptide isolated from the venom of the cone snail Conus geographus. Alpha-conotoxin GIC potently blocks the alpha3beta2 subtype of human nicotinic acetylcholine receptor, showing a high selectivity for neuronal versus muscle subtype [McIntosh, Dowell, Watkins, Garrett, Yoshikami, and Olivera (2002) J. Biol. Chem. 277, 33610-33615]. We have now determined the three-dimensional solution structure of alpha-conotoxin GIC by NMR spectroscopy. The structure of alpha-conotoxin GIC is well defined with backbone and heavy atom root mean square deviations (residues 2-16) of 0.53 A and 0.96 A respectively. Structure and surface comparison of alpha-conotoxin GIC with the other alpha4/7 subfamily conotoxins reveals unique structural aspects of alpha-conotoxin GIC. In particular, the structural comparison between alpha-conotoxins GIC and MII indicates molecular features that may confer their similar receptor specificity profile, as well as those that provide the unique binding characteristics of alpha-conotoxin GIC.

Amino Acid Sequence↗

PubMed2003

Solution conformation of alphaA-conotoxin EIVA, a potent neuromuscular nicotinic acetylcholine receptor antagonist from Conus ermineus.

We report the solution three-dimensional structure of an alphaA-conotoxin EIVA determined by nuclear magnetic resonance spectroscopy and restrained molecular dynamics. The alphaA-conotoxin EIVA consists of 30 amino acids representing the largest peptide among the alpha/alphaA-family conotoxins discovered so far and targets the neuromuscular nicotinic acetylcholine receptor with high affinity. alphaA-Conotoxin EIVA consists of three distinct structural domains. The first domain is mainly composed of the Cys3-Cys11-disulfide loop and is structurally ill-defined with a large backbone root mean square deviation of 1.91 A. The second domain formed by residues His12-Hyp21 is extremely well defined with a backbone root mean square deviation of 0.52 A, thus forming a sturdy stem for the entire molecule. The third C-terminal domain formed by residues Hyp22-Gly29 shows an intermediate structural order having a backbone root mean square deviation of 1.04 A. A structurally ill-defined N-terminal first loop domain connected to a rigid central molecular stem seems to be the general structural feature of the alphaA-conotoxin subfamily. A detailed structural comparison between alphaA-conotoxin EIVA and alphaA-conotoxin PIVA suggests that the higher receptor affinity of alphaA-conotoxin EIVA than alphaA-conotoxin PIVA might originate from different steric disposition and charge distribution in the second loop "handle" motif.

Amino Acid Sequence↗

PubMed2002

Novel alpha-glucosidase inhibitors, CKD-711 and CKD-711a produced by Streptomyces sp. CK-4416. III. Physico-chemical properties and structure elucidation.

We have isolated two novel a-glucosidase inhibitors, O-[4-deoxy-4-(2,3-epoxy-3-hydroxymethyl-4,5,6-trihydroxycyclohexane-1-yl-amino)-alpha-D-glucopyranosyl]-(1-->4)-O-alpha-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranose (named CKD-711) and its hexameric analog CKD-711a, from the fermentation broth of Streptomyces sp. CK-4416. HRFAB-MS and NMR analyses reveal that molecular formulae of CKD-711 and CKD-711a are C25H43NO20 and C37H63NO30, respectively with the latter containing two more glucose moieties than the former. Detailed chemical structures of both compounds have been characterized by high-resolution two-dimensional NMR methods.

Enzyme Inhibitors↗

PubMedDate not supplied

Proteomimetic libraries: design, synthesis, and evaluation of p53-MDM2 interaction inhibitors.

The p53-MDM2 interaction regulates p53-mediated cellular responses to DNA damage, and MDM2 is overexpressed in 7% of all cancers. Structure-based computational design was applied to this system to design libraries centered on a scaffold that projects side chain functionalities with distance and angular relationships equivalent to those seen in the MDM2 interacting motif of p53. A library of 173 such compounds was synthesized using solution phase parallel chemistry. The in vitro competitive ability of the compounds to block p53 peptide binding to MDM2 was determined using a fluorescence polarization competition assay. The most active compound bound with K(d) = 12 microM, and its binding was characterized by (15)N-(1)H HSQC NMR.

Binding Sites↗