Biomedical subjects

Eunice C Y Li-Chan

Publications and source records attributed to Eunice C Y Li-Chan.

11 recordsLinked to original sources

PubMed2007

Production of lactoferricin and other cationic peptides from food grade bovine lactoferrin with various iron saturation levels.

Purification of lactoferricin (Lfcin), a cationic antimicrobial peptide, was achieved by peptic digestion of food grade bovine lactoferrin (LF) followed by fractionation on an industrial grade cation exchange resin with stepwise salt gradient elution. The digest and eluted fractions were partially characterized by MALDI-ToF MS and N-terminal sequencing. A fraction eluted using phosphate buffer with 2.0 M NaCl contained predominantly two peptides with masses of 3196 and 3124 Da, which corresponded to the 26- and 25-amino acid peptides FKCRR WQWRM KKLGA PSITC VRRAF (A), containing the Lfcin sequence. Putative sequences of cationic peptides in other eluted fractions included FKNKS RSFQ, WRMKK LGAPS ITCVR RA, and GAPSI TCVRR AFALE CIRAI AEKKA. The iron saturation level of LF had no effect on the production of Lfcin. Nevertheless, the digestion of LF containing lower iron content led to the production of a higher quantity of low molecular weight cationic peptides. A two-step process using industrial grade cation exchange resin led to 35% recovery of Lfcin and also produced other cationic peptides with potential bioactive properties.

Amino Acid Sequence↗

PubMed2006

Quantitative structure-activity relationship study of bitter peptides.

A database consisting of 224 di- to tetradecapeptides and five amino acids was compiled to study quantitative structure-activity relationships of bitter peptides. Partial least-squares regression-1 analysis was conducted using the amino acid three z-scores and/or three parameters (total hydrophobicity, residue number, and log mass values) as X-variables and bitterness values (log 1/T where T is the bitterness threshold) as Y-variables. Using the three parameters only, significant models (p < 0.001) were obtained describing the entire data set as well as data subsets, except that comprised only of octa- to tetradecapeptides. For data sets comprising different peptide lengths, the models were improved by including the three z-scores at the N-terminal and C-terminal positions. Correlation coefficients for bitterness prediction of 48 dipeptides and 12 pentapeptides were 0.75 (RMSEP = 0.53) and 0.90 (RMSEP = 0.48), respectively. Bulky hydrophobic amino acids at the C terminus and bulky basic amino acids at the N terminus were highly correlated to bitterness.

Amino Acid Sequence↗

PubMed2006

Raman spectroscopy determines structural changes associated with gelation properties of fish proteins recovered at alkaline pH.

Structural changes of alkali-treated rockfish protein isolate (AKPI) during frozen storage were elucidated using a Raman spectrometer and scanning electron microscope (SEM). The results were compared to conventional surimi (CS). No significant textural difference was noted between AKPI stored at pH 5.5 and 7.0. The strongest texture was found for AKPI frozen with cryoprotectants and CS, while the weakest texture was observed in AKPI frozen without cryoprotectants. SEM revealed the most discontinuity in gels of AKPI with no cryoprotectants and a more aggregated microstructure after storage at pH 5.5 than at neutral pH. Raman spectral analysis demonstrated refolding of AKPI by pH readjustment to 7.0, although the refolded structure was not identical to that before the pH shift. CS showed higher alpha-helix content (approximately 50%) than AKPI (approximately 20-30%). Frozen storage induced a decrease and an increase in the alpha-helix content of CS and AKPI samples, respectively. AKPIs were slightly less stable than CS during frozen storage.

Animals↗

PubMed2006

Application of Fourier transform Raman spectroscopy for prediction of bitterness of peptides.

The potential application of Fourier transform (FT) Raman spectroscopy to predict the bitterness of peptides was investigated. FT-Raman spectra were measured for the amino acid Phe and 9 synthetic di-, tri-, and tetra peptides composed of Phe, Gly, and Pro. Partial least squares regression (PLS)-1 analysis was applied to correlate the FT-Raman spectra with bitterness intensity values (R(caf) and log 1/T) reported in the literature. Using full cross-validation, Model 1 based on the single spectral data set for the nine peptides yielded a high correlation coefficient for calibration (R = 0.99), but a low correlation coefficient for prediction (R = 0.56). Two models were constructed using the data sets including replicate spectra for the calibrations and were validated using full cross-validation. Using leave-one-sample-set-out calibrations, Model 2, which was developed with the data for the peptides as well as Phe, yielded a low correlation coefficient (R = 0.533) for the prediction of the bitterness, while Model 3 developed with only the peptide data provided better correlation coefficients (R = 0.807 and 0.724 for R(caf) and log 1/T values, respectively). The correlation coefficients for prediction were 0.975 (R(caf) values) and 0.874 (log 1/T values) for Model 4, which was developed using subtracted spectral data (spectra of peptides with higher R(caf) values minus spectra of peptides with lower R(caf) values). Examination of the PLS regression coefficients at wavenumbers most highly correlated with bitterness revealed the importance of hydrophobicity and peptide length on bitterness. This study indicates the potential of FT-Raman spectroscopy as a useful tool for predicting bitterness of peptides and amino acids.

Amino Acids↗

PubMed2005

Pattern similarity study of functional sites in protein sequences: lysozymes and cystatins.

BACKGROUND: Although it is generally agreed that topography is more conserved than sequences, proteins sharing the same fold can have different functions, while there are protein families with low sequence similarity. An alternative method for profile analysis of characteristic conserved positions of the motifs within the 3D structures may be needed for functional annotation of protein sequences. Using the approach of quantitative structure-activity relationships (QSAR), we have proposed a new algorithm for postulating functional mechanisms on the basis of pattern similarity and average of property values of side-chains in segments within sequences. This approach was used to search for functional sites of proteins belonging to the lysozyme and cystatin families. RESULTS: Hydrophobicity and beta-turn propensity of reference segments with 3-7 residues were used for the homology similarity search (HSS) for active sites. Hydrogen bonding was used as the side-chain property for searching the binding sites of lysozymes. The profiles of similarity constants and average values of these parameters as functions of their positions in the sequences could identify both active and substrate binding sites of the lysozyme of Streptomyces coelicolor, which has been reported as a new fold enzyme (Cellosyl). The same approach was successfully applied to cystatins, especially for postulating the mechanisms of amyloidosis of human cystatin C as well as human lysozyme. CONCLUSION: Pattern similarity and average index values of structure-related properties of side chains in short segments of three residues or longer were, for the first time, successfully applied for predicting functional sites in sequences. This new approach may be applicable to studying functional sites in un-annotated proteins, for which complete 3D structures are not yet available.

Amino Acid Sequence↗

PubMed2005

Angiotensin I converting enzyme inhibitory peptides from in vitro pepsin-pancreatin digestion of soy protein.

Angiotensin I converting enzyme (ACE) inhibitory activity was determined in the soy protein isolate (SPI) digest produced by in vitro pepsin-pancreatin sequential digestion. The inhibitory activity was highest within the first 20 min of pepsin digestion and decreased upon subsequent digestion with pancreatin. An IC(50) value of 0.28 +/- 0.04 mg/mL was determined after 180 min of digestion, while no ACE inhibitory activity was measured for the undigested SPI at 0.73 mg/mL. Chromatographic fractionation of the SPI digest resulted in IC(50) values of active fractions ranging from 0.13 +/- 0.03 to 0.93 +/- 0.08 mg/mL. Although many of the fractions showed ACE inhibition, peptides with lower molecular masses and higher hydrophobicities were most active. The findings show that many different peptides with ACE inhibitory activities were produced after in vitro pepsin-pancreatin digestion of SPI and lead to the speculation that physiological gastrointestinal digestion could also yield ACE inhibitory peptides from SPI.

Amino Acids↗

PubMed2005

Study of protein-lipid interactions at the bovine serum albumin/oil interface by Raman microspectroscopy.

The interface of 10 or 25% (w/v) bovine serum albumin (BSA), pH 7, buffered solution against mineral or corn oil was studied with a Raman microscope. A gradient of distribution of protein and oil at the interface was observed. The difference spectrum obtained by subtracting the spectrum of mineral or corn oil from that of the BSA/oil interface indicated interactions involving different functional groups of the BSA and the oil molecules. Against mineral oil, the BSA spectrum showed reduced intensity of the tryptophan band at 750 cm(-1) and reduced intensity ratio of the tyrosine doublet at 850-830 cm(-1), indicating changes in the microenvironment of these hydrophobic residues. A negative band at 2850 cm(-1) indicated the involvement of the CH groups in the mineral oil. However, the amide regions, normally assigned to protein secondary structure, were not significantly changed. When the spectrum of BSA was subtracted from the BSA/mineral oil interface spectrum, the resultant difference spectrum showed changes of symmetric and antisymmetric CCC stretches at 980 and 1071 cm(-1), respectively. In contrast, the difference spectrum of BSA/corn oil interface - BSA showed a decrease of CH(2) symmetric stretching at 2850 cm(-1) and a decrease of unsaturated fatty acid hydrocarbon chain stretch at 3010 cm(-1). Raman spectroscopy is a useful tool to study the nature of protein-lipid interactions.

Corn Oil↗

PubMed2004

FT-Raman spectroscopy, fluorescent probe, and solvent accessibility study of egg and milk proteins.

Due to possible contribution of both electrostatic and hydrophobic interactions, use of anionic fluorescent probes such as 1-anilinonaphthalene-8-sulfonic acid (ANS) and cis-parinaric acid (CPA) for the measurement of protein surface hydrophobicity (S0) has been controversial. A neutral probe, 6-propionyl-2-(dimethylamino)-naphthalene (PRODAN), may circumvent this problem. To select the best indicator of S0, in this study, the data for nine model proteins in phosphate buffer, pH 7.5, measured using the above-mentioned probes, was compared to their FT-Raman spectra and calculated solvent accessibility values. Log S0 measured using CPA had the highest correlation (r = 0.874) with the intensities of Raman spectral signals at 760 cm(-1) and 2800-3100 cm(-1), which were combined using a mixture design based on the random-centroid optimization. The order of correlation of Raman spectral parameters with S0 values were CPA > PRODAN > ANS. FT-Raman spectroscopy, therefore, identified CPA, followed by PRODAN, as the fluorescent probe of choice for describing surface hydrophobicity. However, the amino acid surface accessibility calculated using the PredictProtein software was not useful in identifying the best fluorescent probe for the measurement of S0.

2-Naphthylamine↗

PubMed2003

Homology similarity analysis of sequences of lactoferricin and its derivatives.

A new method, homology similarity analysis (HSA), was developed to investigate homology pattern similarities of selected segments within sequences of peptides. This new approach facilitated elucidation of the structure-function relationships of lactoferricin derivatives. Helix propensity of positions 4-9 in the lactoferricin sequence was the most important in determining the antimicrobial activity of lactoferricin against Escherichia coli, followed by cationic charge pattern at positions 4-9 and 1-3. The pattern similarity of segments within sequences could be a useful tool for representing the distribution attributes of amino acid residue properties to the structure-function relationships of proteins and peptides, especially when used in conjunction with principal component similarity analysis followed by the regression version of artificial neural networks.

Amino Acid Sequence↗

PubMed2003

Distribution of cadmium-binding components in flax (Linum usitatissimum L.) seed.

The distribution of cadmium- (Cd-) binding components in flaxseed (cultivar NorMan) containing 0.526 ppm (ng/mg) Cd was investigated. Proteins extracted from dehulled, defatted flaxseed were fractionated by anion-exchange and size-exclusion chromatography. The contents of Cd and other metals, UV/visible spectral characteristics, and amino acid compositions of these fractions were analyzed. Over 66% of the eluted Cd was recovered by 0.1 M NaCl elution from DEAE-Sephacel, in a thiol-rich fraction representing only 7% of the extracted proteins. Sephadex G50 size-exclusion chromatography of this 0.1 M NaCl fraction concentrated most of the Cd in a low-molecular-weight peak eluting at V(t). About 72% of the extracted flaxseed proteins eluted from DEAE-Sephacel at 0.25 M NaCl and contained only 25% of the eluted Cd. Because the major Cd-binding fraction is a minor constituent of flaxseed, these results indicate the potential to isolate flaxseed's major storage protein with a low Cd content.

Amino Acids↗

PubMed2002

Principal component similarity analysis of Raman spectra to study the effects of pH, heating, and kappa-carrageenan on whey protein structure.

Raman spectroscopy was used to elucidate structural changes of beta-lactoglobulin (BLG), whey protein isolate (WPI), and bovine serum albumin (BSA), at 15% concentration, as a function of pH (5.0, 7.0, and 9.0), heating (80 degrees C, 30 min), and presence of 0.24% kappa-carrageenan. Three data-processing techniques were used to assist in identifying significant changes in Raman spectral data. Analysis of variance showed that of 12 characteristics examined in the Raman spectra, only a few were significantly affected by pH, heating, kappa-carrageenan, and their interactions. These included amide I (1658 cm(-1)) for WPI and BLG, alpha-helix for BLG and BSA, beta-sheet for BSA, CH stretching (2880 cm(-1)) for BLG and BSA, and CH stretching (2930 cm(-1)) for BSA. Principal component analysis reduced dimensionality of the characteristics. Heating and its interaction with kappa-carrageenan were identified as the most influential in overall structure of the whey proteins, using principal component similarity analysis.

Carrageenan↗