Quantitative structure-activity relationship modeling of peptide and protein behavior as a function of amino acid composition

A quantitative structure-activity relationship (QSAR) modeling approach based on the location of each amino acid along three axes obtained by principal component analysis (called z scores) was extended to physical and functional properties of proteins, where the proportion of particular amino acids rather than a precise sequence is the determining factor. Coomassie Brilliant Blue spectral responses to amino acid homopolymers (R = 0.926) and proteins, either as a function of their contents of six basic and aromatic amino acids (R = 0.976) or as a function of the contributions of these amino acids to the three z scores (R = 0.935), were modeled. The ultraviolet absorbance of proteins was modeled in terms of the z score contributions of tyrosine, tryptophan, and cysteine (R = 0.995). Modeling many protein functional properties in this manner appears to be possible. An approach to modeling peptide behaviors that depend on short sequences of amino acids was also considered.     

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.     

葵花粕中分离蛋白的成分及特性

该文以水酶法提取葵花籽油后的葵花粕为原料，通过盐提酸沉法提取其中的分离蛋白，并对其进行组分分析、氨基酸成分分析、电泳图谱分析和凝胶色谱分析，同时对其溶解性、吸水性、吸油性、乳化性和起泡性等功能特性进行研究。结果显示葵花籽分离蛋白的氨基酸组成与FAO必须氨基酸需要量模式相比赖氨酸含量较低，功能特性好于或接近大豆分离蛋白。葵花分离蛋白含有3个主要组分，其分子量分别为380×10³，100×10³和27×10³，绿原酸与分离蛋白紧密结合。     

Structural requirements of Angiotensin I-converting enzyme inhibitory peptides: quantitative structure-activity relationship study of di- and tripeptides

A database consisting of 168 dipeptides and 140 tripeptides was constructed from published literature to study the quantitative structure--activity relationships of angiotensin I-converting enzyme (ACE) inhibitory peptides. Two models were computed using partial least squares regression based on the three z-scores of 20 coded amino acids and further validated by cross-validation and permutation tests. The two-component model could explain 73.2% of the Y-variance (inhibitor concentration that reduced enzyme activity by 50%, IC50) with the predictive ability of 71.1% for dipeptides, while the single-component model could explain 47.1% of the Y-variance with the predictive ability of 43.3% for tripeptides. Amino acid residues with bulky side chains as well as hydrophobic side chains were preferred for dipeptides. For tripeptides, the most favorable residues for the carboxyl terminus were aromatic amino acids, while positively charged amino acids were preferred for the middle position, and hydrophobic amino acids were preferred for the amino terminus. According to the models, the IC50 values of seven new peptides with matchable primary sequences within pea protein, bovine milk protein, and soybean were predicted. The predicted peptides were synthesized, and their IC50 values were validated through laboratory determination of inhibition of ACE activity.     

Physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate

The amino acid composition and physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were evaluated and compared with those of soy protein isolate (SPI). Edestin, a kind of hexameric legumin, was the major protein component. HPI had similar or higher levels of essential amino acids (except lysine), in comparison to those amino acids of SPI. The essential amino acids in HPI (except lysine and sulfur-containing amino acids) are sufficient for the FAO/WHO suggested requirements for 2-5 year old children. The protein solubility (PS) of HPI was lower than that of SPI at pH less than 8.0 but similar at above pH 8.0. HPI contained much higher free sulfhydryl (SH) content than SPI. Differential scanning calorimetry analysis showed that HPI had only one endothermic peak with denaturation temperature (T(d)) of about 95.0 degrees C, attributed to the edestin component. The T(d) of the endotherm was nearly unaffected by 20-40 mM sodium dodecyl sulfate but significantly decreased by 20 mM dithiothreitol (P < 0.05). The emulsifying activity index, emulsion stability index, and water-holding capacity of HPI were much lower than those of SPI, and the fat adsorption capacity was similar. The data suggest that HPI can be used as a valuable source of nutrition for infants and children but has poor functional properties when compared with SPI. The poor functional properties of HPI have been largely attributed to the formation of covalent disulfide bonds between individual proteins and subsequent aggregation at neutral or acidic pH, due to its high free sulfhydryl content from sulfur-containing amino acids.     

利用HJ-1-A/B CCD2数据反演冬小麦叶面积指数

叶面积指数是十分重要的作物生理生态参数,为提高利用国产环境减灾小卫星CCD数据反演冬小麦叶面积指数的精度,该文以5种常用的植被指数(归一化差值植被指数(normalized difference vegetation index,NDVI),增强植被指数(enhanced vegetation index,EVI),双波段增强植被指数(2-bands enhanced vegetation index,EVI2),比值植被指数(ratiovegetation index,RVI),土壤调节植被指数(soil-adjusted vegetation index,SAVI)为基础,结合3种常用的回归模型,按生长阶段比较分析了不同植被指数和回归模型反演叶面积指数的精度。结果表明,除生殖生长阶段外,叶面积指数和5种植被指数之间均有较强的相关关系;指数模型和一元线性模型分别为全生育期和营养生长阶段的最佳拟合模型;EVI在全生育期拟合时的表现好于其他4个指数(R2=0.9348),SAVI则是营养生长阶段表现最佳的指数(R2=0.9404)。该研究为进一步利用植被指数反演叶面积指数提供了参考。     

Comparison of physicochemical properties of 7S and 11S globulins from pea, fava bean, cowpea, and French bean with those of soybean--French bean 7S globulin exhibits excellent properties

Legume seeds contain 7S and/or 11S globulins as major storage proteins. The amino acid sequences of them from many legumes are similar to each other in the species but different from each other, meaning that some of these proteins from some crops exhibit excellent functional properties. To demonstrate this, we compared protein chemical and functional properties (thermal stability, surface hydrophobicity, solubility as a function of pH, and emulsifying properties) of these proteins from pea, fava bean, cowpea, and French bean with those of soybean as a control at the same conditions. The comparison clearly indicated that the 7S globulin of French bean exhibited excellent solubility (100%) at pH 4.2-7.0 even at a low ionic strength condition (mu = 0.08) and excellent emulsion stability (a little phase separation after 3 days) at pH 7.6 and mu = 0.08, although the emulsions from most of the other proteins separated in 1 h. These results indicate that our assumption is correct.     

可食性魔芋葡甘聚糖耐水耐高温复合膜的制备及性能研究

以魔芋胶（KG）即魔芋葡甘聚糖（KGM）为基材，在碱性条件下加热制备耐水耐高温膜，采用5因素（1/2实施）二次正交旋转组合设计研究了石蜡、硬脂酸、乳化剂、甘油和聚乙二醇400对膜水蒸气透过系数（WVP）、耐破度（BS）、抗张强度（TS）和伸长率（E）的影响，得到相应单指标二次回归模型。分析表明：5个因素的一次项，二次项及交互项对膜的WVP、BS、TS和E均有不同程度的影响。得出了各因子对膜性能的影响规律。     

Properties of protein powders from arrowtooth flounder (Atheresthes stomias) and herring (Clupea harengus) byproducts

Functional, nutritional, and thermal properties of freeze-dried protein powders (FPP) from whole herring (WHP), herring body (HBP), herring head (HHP), herring gonad (HGP), and arrowtooth flounder fillets (AFP) were evaluated. The FPP samples have desirable nutritional and functional properties and contained 63-81.4% protein. All FPP samples had desirable essential amino acid profiles and mineral contents. The emulsifying and fat adsorption capacities of all FPP samples were higher than those of soy protein concentrate. The emulsifying stability of WHP was lower than that of egg albumin but greater than that of soy protein concentrate. Thermal stability of the FPP samples is in the following order: HGP > HBP > WHP > HHP > AFP.     

Characterization of soluble amaranth and soybean proteins based on fluorescence, hydrophobicity, electrophoresis, amino Acid analysis, circular dichroism, and differential scanning calorimetry measurements.

Intrinsic fluorescence (IF), surface hydrophobicity (S(o)), electrophoresis, amino acid analysis, circular dichroism (CD), and differential scanning calorimetry (DSC) were used to study folded and unfolded soluble proteins from Amaranthus hypochondriacus (A. h.) and soybean (S). Globulin (Glo) and albumin subfractions (Alb-1 and Alb-2) were extracted from A. h. and S and denatured with urea. Electrophoretic and functional properties indicated a significant correlation between soluble protein fractions from soybean and amaranth. The protein fractions shared some common electrophoretic bands as well as a similar amino acid composition. The larger percent of denaturation in protein fractions, which is associated with enthalpy and the number of ruptured hydrogen bonds, corresponds to disappearance of alpha-helix. The obtained results provided evidence of differences in their secondary and tertiary structures. The most stable was Glo followed by the Alb-2 fraction. Predicted functional changes in model protein systems such as pseudocereals and legumes in response to processing conditions may be encountered in pharmaceutical and food industries. These plants can be a substitute for some cereals.     

Studies of Partial Amino Acid Sequences of γ‐40k Secalins of Rye

Though γ‐40k secalins are a major protein type within rye storage proteins, total amino acid sequences are not as well known as the gluten proteins of wheat. Well‐reputed structural features such as amino acid compositions and molecular masses indicated a close relationship between γ‐40k secalins and γ‐gliadins of wheat, but the degree of homology of amino acid sequences and the positions of intramolecular disulfide bonds are unknown. Therefore, two major components of γ‐40k secalins (R1, R2) were analyzed for partial amino acid sequences. The R1 and R2, derivatized with 4‐vinylpyridine, were isolated from the prolamin fraction of rye cultivar Danko by means of a two‐step RP‐HPLC on C₁₈ silica gel. The proteins were digested in parallel with trypsin and thermolysin, and the partial hydrolyzates were separated by RP‐HPLC. Simultaneous measurement of UV absorbance at 210 and 254 nm allowed the detection of all peptides eluted as well as the specific detection of pyridylethylated cysteine peptides. Isolated peptides were characterized by sequence analysis, and in parts by mass spectrometry, and assigned to known sequences of γ‐gliadins. The results demonstrated that the N‐terminal domain of R1 and R2 remained undigested after tryptic hydrolysis; they were in agreement with the N‐terminal domain of γ‐gliadins in their molecular masses and in the absence of cysteine residues. Most of the isolated peptides originated from the C‐terminal domains, they covered 83% (R1) and 77% (R2), respectively, of the C‐terminal domain of a known γ‐gliadin (clone pW1020). Comparison of R1 and R2 revealed differences only in a few sequence positions. The degree of homology between the C‐terminal domains present in γ‐40k secalins and γ‐gliadins was ≈85%. All eight cysteine residues of γ‐gliadins were found in R1 and R2 sequences. Remarkably, sequences close to corresponding cysteine residues were identical for γ‐40k secalins and γ‐gliadins. Therefore, it can be assumed that the positions of intramolecular disulfide links are homologous.     

Physicochemical and Functional Characterization of Protein Isolated from Different Quinoa Varieties (Chenopodium quinoa Willd.)

The objectives of this work were to investigate the nutritional and physicochemical characteristics as well as the functional properties of quinoa protein isolates (QPI) from different varieties, and to determine their potential use of such protein isolates in food products. Proteins were isolated by isoelectric precipitation at pH 5 from quinoa flour, and the QPI had a protein percentage of over 85%. The comparison of the flours and QPI electrophoretic profiles indicated that the extraction method allowed isolating practically all proteins of each variety. All the varieties analyzed had high lysine content, compared with cereals, and the essential amino acid content of Bolivian varieties was higher than varieties from Peru. The pH value affected the solubility and foaming capacity, and the magnitude of effects depended on the variety. Cluster analysis showed a strong influence of variety source and amino acid composition on protein physicochemical and functional properties; samples from Bolivia (cluster 2) were characterized as having the highest thermal stability, oil binding capacity, and water binding capacity at acid pH; samples from Peru (cluster 1) had the highest water binding capacity at basic pH and foaming capacity at pH 5. QPI presented a potential as an alternative vegetable protein for food application, in particular for vegetarian and vegan diets.     

Effect of pH and temperature on comparative nonenzymatic browning of proteins produced by oxidized lipids and carbohydrates

Bovine serum albumin (BSA) was incubated for 24 h in the presence of 10 mM ribose (RI), methyl linoleate hydroperoxides, or the secondary products of methyl linoleate oxidation (SP), at five temperatures (25, 37, 50, 80, and 120 degrees C) and different pHs (4, 7, and 10), to study the influence of these variables in the browning, fluorescence, amino acid losses, and pyrrolization of the modified proteins. All treated proteins exhibited similar colors and fluorescence spectra, and the spectra of their Ehrlich adducts were also analogous. However, at 25-50 degrees C the proteins treated with oxidized lipids exhibited higher color changes, amino acid losses, and pyrrolization than the BSA treated with RI, and these effects were much higher in proteins treated with RI at 80-120 degrees C. The effect of pH was similar in proteins treated with RI or SP. These results suggested a similarity for browned proteins obtained from both carbohydrates and oxidized lipids. In addition, both reactions seem to be complementary, because melanoidin formation derived from oxidized lipids can be produced under conditions different from those carbohydrate/protein reactions.     

Bound fumonisin B1: analysis of fumonisin-B1 glyco and amino acid conjugates by liquid chromatography-electrospray ionization-tandem mass spectrometry

To study the formation of fumonisin artifacts and the binding of fumonisins to matrix components (e.g., saccharides and proteins) in thermal-treated food, model experiments were performed. Fumonisin B(1) and hydrolyzed fumonisin B(1) were incubated with alpha-d-glucose and sucrose (mono- and disaccharide models), with methyl alpha-d-glucopyranoside (starch model), and with the amino acid derivatives N-alpha-acetyl-l-lysine methyl ester and BOC-l-cysteine methyl ester (protein models). The reaction products formed were analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry. The incubation of d-glucose with fumonisin B(1) or hydrolyzed fumonisin B(1) resulted in the formation of Amadori rearrangement products. Whereas conjugates were found following the reaction of sucrose, methyl alpha-d-glucopyranoside, and the amino acid derivatives with fumonisin B(1), the heating with hydrolyzed fumonisin B(1) yielded no artifacts. For structural determination, the stable reaction product formed by heating of methyl alpha-d-glucopyranoside (as starch model) with fumonisin B(1) was purified and identified by nuclear magnetic resonance spectroscopy as the diester of the fumonisin tricarballylic acid side chains with methyl alpha-d-glucopyranoside. These model experiments demonstrate that fumonisins are able to bind to polysaccharides and proteins via their two tricarballylic acid side chains.     

亚东黑耳的氨基酸特征分析及蛋白质品质评价

亚东黑耳(Exidia sp.)是一种尚未实现人工栽培的珍稀食用菌,为发掘和利用其营养价值,在现行国际氨基酸模式谱的基础上,以氨基酸评分(AAS)、美国国家科学院医学研究所(IOM)模式评分、化学评分(CS)、氨基酸比值系数(RC)、氨基酸比值系数分(SRC)和必需氨基酸指数(EAAI)等多个参数为指标,系统地分析了亚东黑耳的氨基酸特征和蛋白质品质。结果表明,亚东黑耳中含有18种常见氨基酸,包括全部8种必需氨基酸;其粗蛋白含量与粮食作物接近,蛋白质中必需氨基酸含量充足(473.4 mg·g^-1 pro),其中亮氨酸含量较高(67.73 mg·g^-1 pro)。参数评估表明,亚东黑耳蛋白质中的必需氨基酸比例相对合理(RC值0.74～1.66,EAAI值129.11),基本符合国际推行的氨基酸平衡模式谱(AAS值均高于98.75%,IOM模式评分均高于100%),是相对优质的蛋白质,但其平衡性和含量均逊色于鸡蛋蛋白(CS值70.93%～128.30%)。本研究结果为进一步开发野生菌资源提供了科学基础。     

Prediction of molar extinction coefficients of proteins and peptides using UV absorption of the constituent amino acids at 214 nm to enable quantitative reverse phase high-performance liquid chromatography-mass spectrometry analysis

The molar extinction coefficients of 20 amino acids and the peptide bond were measured at 214 nm in the presence of acetonitrile and formic acid to enable quantitative comparison of peptides eluting from reversed-phase high-performance liquid chromatography, once identified with mass spectrometry (RP-HPLC-MS). The peptide bond has a molar extinction coefficient of 923 M(-1) cm(-1). Tryptophan has a molar extinction coefficient that is approximately 30 times higher than that of the peptide bond, whereas the molar extinction coefficients of phenylalanine, tyrosine, and histidine are approximately six times higher than that of the peptide bond. Proline, as an individual amino acid, has a negligible molar extinction coefficient. However, when present in the peptide chain (except at the N terminus), it absorbs approximately three times more than a peptide bond. Methionine has a similar molar extinction coefficient as the peptide bond, while all other amino acids have much lower molar extinction coefficients. The predictability of the molar extinction coefficients of proteins and peptides, calculated by the amino acid composition and the number of peptide bonds present, was validated using several proteins and peptides. Most of the measured and calculated molar extinction coefficients were in good agreement, which shows that it is possible to compare peptides analyzed by RP-HPLC-MS in a quantitative way. This method enables a quantitative analysis of all peptides present in hydrolysates once identified with RP-HPLC-MS.     

Functional properties of guava seed glutelins

Five guava seed glutelin extracts were obtained with different buffer solutions: Na(2)B(4)O(7) alone (Glut.Bo) or containing SDS (Glut.BoSDS), 2-mercaptoethanol (Glut.Bo2-ME), or a combination of both (Glut.BoSDS2-ME) and NaOH (Glut.Na). All borate buffer solutions were at pH 10. The higher yield of glutelins corresponded to the Glut.BoSDS extract (81.9% dry basis) and the lower to Glut.Bo (6.8%). The functional properties of the five guava seed glutelin extracts were determined. Glut.BoSDS, Glut.BoSDS2-ME, and Glut.Na showed high values for several properties, including surface hydrophobicity (7.7, 10.8, and 0.6, respectively), solubility at pH 10 (91.1, 77.9, and 96.7, respectively), water-holding capacity at pH 3.6 (1.7, 2.5, and 2.8, respectively), emulsifying activity index (pH 10; 503.5, 238.2, and 838.0, respectively), and foaming properties (pH 10; V(0) = 0.14, 0.25, and 0.19, respectively; V(max) = 6.1, 5.59, and 4.51, respectively; t(1/2) = 266, 255.3, and 94 s, respectively). These results suggest that the denaturing reagent (SDS or NaOH) during extraction conferred on the proteins a structure that facilitated the development of their functional properties.     

Characterization and crystallography of recombinant 7S globulins of Adzuki bean and structure-function relationships with 7S globulins of various crops

The recombinant proteins Adzuki 7S1, Adzuki 7S2, and Adzuki 7S3 were prepared through the Escherichia coli expression systems of three kinds of adzuki bean cDNAs. The recombinant proteins exhibited intrinsic thermal stabilities, surface hydrophobicities, and solubilities, although the homology of their amino acid sequences ranged from 95-98%. To understand why these individual proteins exhibited different properties, their three-dimensional structures were elucidated. The three proteins were successfully crystallized, and the three-dimensional structures of Adzuki 7S1 and Adzuki 7S3 were determined. The properties and structures of these two proteins were comprehensively compared with those of recombinant 7S globulins (soybean beta-conglycinins beta and alpha'c and mungbean 8Salpha) reported previously. It was likely that cavity sizes, hydrogen bonds, salt bridges, hydrophobic interactions, and lengths of loops determine the thermal stabilities of 7S globulins, and results indicated that cavity sizes strongly contribute to such stability. Surface hydrophobicity was also found to be determined not only by distributions of hydrophobic residues on the molecular surface. Furthermore, solubility at neutral and weak alkaline pH values at mu = 0.08 was found to be dominantly influenced by the electrostatic surface potentials.     

Proteins Extracted from Defatted Wheat Germ: Nutritional and Structural Properties

The main by‐product of the wheat germ oil extraction process is a defatted wheat germ meal, which has a relatively high protein content, making it an attractive and promising source of vegetable proteins. Four protein fractions (albumin, globulin, prolamine, and glutelin) and protein isolate from defatted wheat germ flour (DWGF) were fractionated and then characterized by amino acid analysis, SDS‐PAGE, and differential scanning calorimetry (DSC). Albumin was the major fraction (34.5%) extracted, followed by globulin (15.6%), glutelin (10.6%), and prolamine (4.6%). Protein isolate was mainly composed of albumin and globulin. These protein fractions and protein isolate showed an excellent balance of all essential amino acids, with a relatively high level of glutamic acid, arginine, leucine, and glycine, whereas cystine was lacking. All the estimated nutritional quality parameters based on amino acids composition showed that defatted wheat germ proteins had good nutritional quality. Nonreduced and reduced SDS‐PAGE analyses showed that S‐S bonds ere deficient in the structure of wheat germ proteins. The albumin fraction consisted of 19 major polypeptide bands with M_r 14,000–84,000. The globulin fraction showed four distinct polypeptides or polypeptide group bands with M_r 55,000, 37,000–43,000, 24,000, and 12,000–20,000, which may be the components of the 8S‐type and 11S‐like proteins. The prolamine fraction showed a predominant doublet‐like band at M_r 17,000–16,000, while the glutelin fraction showed five major polypeptide bands with M_r 39,000, 20,000, 18,000, 17,000, and 14,000. Protein isolate and DWGF showed very similar SDS‐PAGE patterns. Except for prolamine and glutelin fractions without detectable calorimetric response, the globulin fraction possessed the highest thermal stability (T_d = 83.80°C, ΔH =1.36 J/g ), followed by protein isolate (T_d = 80.05°C, ΔH = 0.76 J/g), while the albumin fraction was lowest (T_d = 69.72°C, ΔH = 0.53 J/g). The findings on defatted wheat germ proteins are important for their potential application as functional food ingredients.     

基于无人机图像分割的冬小麦叶绿素与叶面积指数反演

叶绿素含量与叶面积指数是反映作物长势的重要理化参数,准确、高效定量估计小麦叶绿素含量与叶面积指数对于产量预测和田间管理决策具有重要意义,无人机(Unmanned Aerial Vehicle,UAV)遥感影像具有高空间分辨率的优势,被广泛应用于作物理化参数反演,但现有叶绿素含量与叶面积指数反演模型受土壤、阴影等背景噪声...