• Composites Research
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• v.33 no.3
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• pp.169-175
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• 2020

The compression and tension test were performed to evaluate the stiffnesses of the conical composite lattice structures and results of test were compared with finite element analysis results. Because of difficulty to perform simple tension and compression test due to conical shape, suitable specimens and jig for test were made. Subelements extracted from the structure were prepared for compression test. Compression test of subelement was performed and compressive strains in fiber direction were measured. Compressive stiffness of the helical rib was verified by finite element analysis results. For stiffness of hoop rib, hoop ring specimens were extracted from the structure. Tension test of hoop ring specimen was performed to apply bending deformation to hoop rib. Stiffness of hoop rib was verified by finite element model considering various fiber volume fraction in thickness direction.

• Bulletin of the Korean Chemical Society
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• v.24 no.10
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• pp.1478-1484
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• 2003

CRAMP was identified from a cDNA clone derived from a mouse femoral marrow cells as a member of cathelicidin-derived antimicrobial peptide. Tertiary structure of CRAMP in TFE/$H_2O$ (1 : 1, v/v) solution has been determined by NMR spectroscopy previously and consists of two amphipathic $\alpha-helices$ from Leu4 to Lys10 and from Gly16 to Leu33. These two helices are connected by a flexible region from Gly11 to Gly16. Analysis of series of fragments composed of various portion of CRAMP revealed that an 18-residue fragment with the sequence from Gly16 to Leu33 (CRAMP-18) was found to retain antibacterial activity without cytotoxicity. The effects of two Phe residues at positions 14 and 15 of CRAMP-18 on structure, antibacterial activity, and interaction with lipid membranes were investigated by $Phe^{14,15}$ ${\rightarrow}$ Ala substitution (CRAMP-18-A) in the present study. Substitution of Phe with Ala in CRAMP-18 caused a significant reduction on antibacterial and membrane-disrupting activities. Tertiary structures of CRAMP-18 in 50% TFE/$H_2O$ (1 : 1, v : v) solution shows amphipathic ${\alpha}$-helix, from $Glu^2{\;}to{\;}Leu^{18}$, while CRAMP-18-A has relatively short amphipathic ${\alpha}$-helix from $Leu^4{\;}to{\;}Ala^{15}$. These results suggest that the hydrophobic property of $Phe^{14}{\;}and{\;}Phe^15$ in CRAMP-18 is essential for its antibacterial activity, ${\alpha}$-helical structure, and interactions with phospholipid membranes.

• Molecules and Cells
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• v.21 no.2
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• pp.229-236
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• 2006

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 $7.3{\AA}$, which suggests that the minimal oligomer structure responsible is a pentamer.

• Microbiology and Biotechnology Letters
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• v.31 no.4
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• pp.311-321
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• 2003

Bacteria produce lipases, which can catalyze both the hydrolysis and the synthesis of long chain triglycerides. These reactions usually proceed with high regioselectivity and enantioselectivity, and, therefore, lipases have become very important biocatalysts used in organic chemistry. 3D lipase structures were solved from several bacterial lipases. They have an $\alpha/\beta$ hydrolase fold and a catalytic triad consisting of a nucleophilic serine, and an aspartate or glutamate residue that is hydrogen bonded to a histindine. Active sites are covered with $\alpha$-helical lid structure, of which movement is involved in the enzyme's activation at oil/water interface. Four substrate binding pockets were identified for triglycerides: an oxyanion hole and three pockets accommodating the fatty acids bound at positions sn-1, sn-2, and sn-3. These pockets determine the enantiopreference of a lipase. The understanding of structure-function relationships as well as the development of molecular evolution techniques will enable researchers to tailor new lipases for biotechnological applications.

• Journal of Microbiology and Biotechnology
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• v.26 no.6
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• pp.1046-1056
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• 2016

RV-23 is a melittin-related antibacterial peptide (MRP) with lower cytotoxicity than either melittin or AR-23, another MRP. The aim of this study was to explore the mechanism of RV-23's antibacterial selectivity and its hemocompatibility. The results showed that all the peptides exhibited lytic activity against Staphylococcus aureus and Escherichia coli, with RV-23 showing the highest potency. Moreover, RV-23 had lower cytotoxicity than melittin or AR-23 at their minimal inhibitory concentration. In addition, CD experiments showed that melittin, RV-23, and AR-23 all had a typical α-helical structure, and RV-23 had the lowest α-helix content. The structural information showed that RV-23 has the lowest hydrophobicity and highest hydrophobic moment. Because hydrophobicity and α-helix content are believed to correlate with hemolysis, the results indicate that the selective lytic activity against bacteria of RV-23 may be due to its low hydrophobicity and α-helicity, which lead to low cytotoxicity without affecting antibacterial activity. Furthermore, RV-23 did not affect the structure and function of blood components such as red blood cells, platelets, albumin, and the blood coagulation system. In conclusion, RV-23 is a cell-selective antibacterial peptide with high hemocompatibility due to its unique structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.8
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• pp.2601-2610
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• 1996

Surface protrusions have been attached on a cylinder surface to reduce the flow-induced structural vibration by controlling the wake flow. Wind tunnel tests on the near wake of a circular cylinder with surface protrusions were carried out to investigate the flow characteristics of the controlled wake. Three experimental models were used in this experiment; one plain cylinder of diameter D and two cylinders wrapped helically by three small wires of diameter d=0.075D with pitches of 5D and 10D, respectively. Free stream velocity was ranged to have Reynolds number from 5000 to 50,000. Streamwise and vertical velocity components of the wake were measured by a hot-wire anemometry. The spanwise velocity component measured by a one-component fiber optic LDV revealed that time-averaged wake field has a nearly two-dimensional structure. It was found that the surface protrusions elongate the vortex formation region, which decrease the vortex shedding frequency. The suppression of vortices caused by the surface protrusions increases the velocity deficit in the center of wake region.

• International Journal of Fluid Machinery and Systems
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• v.3 no.2
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• pp.129-136
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• 2010

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of flow field between in the cavitating and no-cavitating conditions.

• Journal of Microbiology and Biotechnology
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• v.20 no.8
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• pp.1192-1195
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• 2010

To investigate the influence of the N- or C-terminal regions of pleurocidin (Ple) peptide on antifungal activity, four analogs partially truncated in the N- or C-terminal regions were designed and synthesized. Circular dichroism (CD) spectroscopy demonstrated that all the analogs maintained an alpha-helical structure. The antifungal susceptibility testing also showed that the analogs exhibited antifungal activities against human fungal pathogens, without hemolytic effects against human erythrocytes. The result further indicated that the analogs had discrepant antifungal activities [Ple>Ple (1-22)>Ple (4-25)>Ple (1- 19)>Ple (7-25)] and that N-terminal deletion affected the activities much more than C-terminal deletion. Hydrophobicity [Ple>Ple (1-22)>Ple (4-25)>Ple (1-19)> Ple (7-25)] was thought to have been one of the consistent factors that influenced these activity patterns, rather than the other primary factors like the helicity [Ple>Ple (4-25) >Ple (1-22)>Ple (1-19)>Ple (7-25)] or the net charge [Ple=Ple (4-25)=Ple (7-25)>Ple (1-22)=Ple (1-19)] of the peptides. In conclusion, the hydrophobic amino acids in the N-terminal region of Ple is more crucial for antifungal activity than those in the C-terminal region.

• Journal of Microbiology and Biotechnology
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• v.20 no.1
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• pp.54-62
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• 2010

A novel harpin-like protein, HpaXm, was described from cotton leaf blight bacteria, Xanthomonas citri subsp. malvacearum. The hpaXm was found to be localized between hrp2 and hrcC. A phylogenetic analysis of the complete amino acid sequence or solely the 13 highly conserved residues $H_2N$-SEKQLDQLLTQLI-COOH in the N-terminal $\alpha$-helix indicates that HpaXm is evolutionarily closer to HpaGXag and HpaXac than to Hpa1Xoo and Hpa1Xoc. A synthesized peptide containing two heptads, 39-LDQLLTQLIMALLQ-52, from the N-terminal a-helical region of HpaXm displayed comparable activity in inducing a hypersensitive response, but two other synthesized derivatives, $HpaXm{\Delta}T44C$ and $HpaXm{\Delta}M48Q$, showed reduced HR-triggering activity. The data from a GST trap test revealed that HpaXm was released into the extracellular medium, hpaXm mutant deficient for the leader peptide (1-MNSLNTQIGANSSFL-15) was unable to be secreted outside cells but still induced HR in tobacco leaves.

• Journal of the Korean Magnetic Resonance Society
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• v.7 no.1
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• pp.37-45
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• 2003

Human CD99 is a ubiquitous 32-kDa transmembrane protein encoded by mic2 gene. Recently it has been reported that expression of a splice variant of CD99 transmembrane protein (Type I and Type II) increases invasive ability of human breast cancer cells. To understand structural basis for cellular functions of CD99 Type II, we have initiated studies on hCD99$\^$TMcytoI/ using circular dichroism (CD) and multi-dimensional NMR spectroscopy. CD spectrum of hCD99$\^$TMytoI/ in the presence of 200mM DPC and CHAPS displayed an existence ${\alpha}$-helical conformation, showing that it could form an ${\alpha}$-helix under membrane environments. In addition, we have found that the cytoplasmic domain of CD99 would form symmetric dimmer in the presence of transmembrane domain. Although it has been rarely figured out the correlation between structure and functional mechanism of hCD99$\^$TMcytoI/, the dimerization or oligomerization would play an important role in its biological function.