Pfeffer P E, Osman S F, Hotchkiss A, Bhagwat A A, Keister D L, Valentine K M
U.S. Department of Agriculture, ARS, Eastern Regional Research Center, Wyndmoor, PA 19038, USA.
Carbohydr Res. 1996 Dec 24;296:23-37. doi: 10.1016/s0008-6215(96)00238-8.
A unique glucan has been isolated from a recombinant strain of a Rhizobium meliloti TY7, a cyclic beta-(1-->2) glucan mutant carrying a locus specifying beta-(1-->3; 1-->6) glucan synthesis from Bradyrhizobium japonicum USDA110. This compound, which appears to have considerable hydrophobic affinity, was separated from a perchloric acid cell extract by adsorption to a C-18 silica column. Unlike those cyclic glucans previously isolated from Rhizobium meliloti or Bradyrhizobium japonicum, this molecule contains neither phosphoglycerol nor phosphocholine substituents, respectively. 2D NMR, FAB mass spectrometric analysis and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) confirmed that this glucan is a single, cyclic decasaccharide (cyclolaminarinose) in which one of the residues is substituted in its 6-position with beta-laminarabiose. This structural assignment was confirmed by mass spectral and NMR analyses of the product obtained from two consecutive Smith degradations. Unlike the complex 13C spectrum of the unoxidized material, the spectrum of this product consisted of only six resonances due to rapid time averaging of its symmetrical structure on the relatively slow NMR timescale. Synthesis of this newly described cyclic beta-glucan in the R. meliloti ndvB mutant restored the symbiotic and hypoosmotic adaptation characteristics of the R. meliloti wild type strain.
一种独特的葡聚糖已从苜蓿根瘤菌TY7的重组菌株中分离出来，该菌株是一种环状β-(1→2)葡聚糖突变体，携带一个指定来自慢生根瘤菌USDA110的β-(1→3; 1→6)葡聚糖合成的基因座。这种化合物似乎具有相当大的疏水亲和力，通过吸附到C-18硅胶柱上从高氯酸细胞提取物中分离出来。与先前从苜蓿根瘤菌或慢生根瘤菌中分离出的那些环状葡聚糖不同，该分子分别既不含有磷酸甘油也不含有磷酸胆碱取代基。二维核磁共振、快原子轰击质谱分析以及带有脉冲安培检测的高效阴离子交换色谱法（HPAEC-PAD）证实，这种葡聚糖是一种单一的环状十糖（环层孔菌素糖），其中一个残基在其6位被β-层孔二糖取代。通过对两次连续的史密斯降解得到的产物进行质谱和核磁共振分析，证实了这一结构归属。与未氧化材料复杂的13C谱不同，该产物的谱由于其对称结构在相对较慢的核磁共振时间尺度上的快速时间平均，仅由六个共振峰组成。在苜蓿根瘤菌ndvB突变体中合成这种新描述的环状β-葡聚糖恢复了苜蓿根瘤菌野生型菌株的共生和低渗适应特性。
