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首页> 外文期刊>Biomacromolecules >Acacia Senegal Gum:Continuum of Molecular Species Differing by Their Protein to Sugar Ratio,Molecular Weight,and Charges
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Acacia Senegal Gum:Continuum of Molecular Species Differing by Their Protein to Sugar Ratio,Molecular Weight,and Charges

机译：塞内加尔阿拉伯胶：蛋白质，糖分，分子量和电荷不同的分子物种的连续体

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The main chemical and physical features of the Acacia Senegal exudate gum and its molecular fractions isolated by chromatographies were determined using a wide variety of methods.Three main molecular fractions were isolated after hydrophobic interaction chromatography (HIC) and biochemical analyses confirmed the presence of an arabinogalactan-peptide (FI),an arabinogalactan-protein (FII),and a glycoprotein (FIII) fraction as described commonly in the literature.Further purification of FIII using size exclusion chromatography revealed three distinct populations.A wide molecular weight distribution within each population with the presence of at least two distinct molecular species per population was identified by high performance size exclusion chromatography coupled to on line multi-angle laser light scattering (HPSEC-MALLS).In addition,both sugars content (neutral and uronic acids) and UV profiles revealed that FIII was composed of a continuum of molecular species differing both by their protein-to-sugar ratio and molecular weight.FI and FII had average molecular weight M_w of 2.86 x 10~5 and 1.86 x 10~6 g cebtre dit rnol~(-1),respectively,and a low polydispersity index (M_w/M_n approx 1.3).The three populations identified in FIII after HIC separation had M_w of 2.67 x 10~6,7.76 x 10~5,and 2.95 x 10~5 g cebtre dit mol~(-1) and very low polydispersity indexes (1.13,1.04,and 1.01).Estimation of the polypeptide backbone length in the three fractions gave 43,2253,and 4443 amino acid residues,respectively,hydroxyproline (Hyp) and serine being the most prominent residues within FI and FII,Hyp and Asx (asparagine+aspartic acid) within FIII.Secondary structure prediction from circular dichroism data resulted in polyproline II,beta-sheet,and random coil structures for FII and FIII,whereas no secondary structure was identified in FI.The existence of exposed tryptophanyl residues to the solvent was noticed by fluorescence in FII and FIII,tryptophan residues being absent from FI.In addition,8-5' non cyclic diferulic acid was identified to be covalently linked to carbohydrate moieties of FII.Infrared spectroscopy identified the different vibrations of saccharidic and peptidic bonds with absorbance amplitudes in agreement with sugar and protein elementary analyses.Titration measurements in order to evaluate the number of charges on total Acacia gum and its molecular fractions revealed that 100% of charges came from poly saccharidic moieties (i.e.,glucuronic acids) in FI.Charges coming from polysaccharidic moieties were of 91.3% and 37.9% for FII and FIII,respectively,the remaining 8.7% and 62.1% charges in FII and FIII molecular fractions coming from the polypeptidic backbone.
机译：塞内加尔相思树胶质渗出胶的主要化学和物理特征以及通过色谱法分离出的分子组分的测定方法多种多样。疏水相互作用色谱法（HIC）分离出三个主要分子组分，生化分析证实了阿拉伯半乳聚糖的存在-肽（FI），阿拉伯半乳聚糖蛋白（FII）和糖蛋白（FIII）组分，如文献所述。使用尺寸排阻色谱法进一步纯化FIII显示出三个不同的种群。通过高效尺寸排阻色谱联用在线多角度激光散射（HPSEC-MALLS），鉴定出每个种群至少存在两种​​不同的分子种类。此外，糖含量（中性和糖醛酸）和紫外线分布图揭示了FIII是由分子种类的连续体组成的，两者的区别在于FI和FII的平均分子量M_w分别为2.86 x 10〜5和1.86 x 10〜6 g cebtre dit rnol〜（-1），且多分散指数（M_w / M_n约为1.3）.HIC分离后在FIII中鉴定出的三个种群的M_w为2.67 x 10〜6、7.76 x 10〜5和2.95 x 10〜5 g cebtre dit mol〜（-1），并且多分散指数非常低（1.13、1.04和1.01）。估算这三个馏分的多肽骨架长度分别为43,2253和4443个氨基酸残基，羟脯氨酸（Hyp）和丝氨酸分别是FI和FII，Hyp和FII中最突出的残基。 FIII中的Asx（天冬酰胺+天冬氨酸）。根据圆二色性数据预测的二级结构产生FII和FIII的聚脯氨酸II，β-折叠和随机卷曲结构，而FI中未鉴定出二级结构。存在暴露的色氨酸残基通过FII和FIII中的荧光观察到溶剂的残留，F中不存在色氨酸残基此外，还确定了8-5'非环状二阿魏酸与FII的碳水化合物部分共价连接。红外光谱鉴定了糖和肽键的不同振动，其吸收幅度与糖和蛋白质元素分析相符。为了评估整个相思树胶的电荷数量及其分子组成，我们发现100％的电荷来自FI中的多糖部分（即葡萄糖醛酸），而多糖部分的电荷分别为91.3％和37.9％ FII和FIII分别在FII和FIII分子级分中剩余的8.7％和62.1％电荷来自多肽骨架。

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