Hartland R P, Emerson G W, Sullivan P A
Biochemistry Department, University of Otago, Dunedin, New Zealand.
Proc Biol Sci. 1991 Nov 22;246(1316):155-60. doi: 10.1098/rspb.1991.0138.
A Mr 34,000 wall protein was isolated as a by-product of the purification of an endo-(1-3)-beta-glucanase from the culture filtrate of Candida albicans. The purified fraction contained no exo- or endo-beta-glucanase activity, and analysis by SDS poly-acrylamide gel electrophoresis (SDS-PAGE) showed one protein band at Mr 34,000. Analysis by gel filtration high performance liquid chromatography (HPLC) of reaction products from incubations of the protein fraction with laminarioligosaccharides of five glucosyl units or greater revealed a unique glucanosyl transferase activity. The enzyme specifically cleaved laminaribiaose (G2) from the reducing-end of a linear beta-(1-3)-glucan and transferred the remainder to another laminarioligosaccharide. The reaction with laminaripentaose (G5) produced G2 and a product eluting at the position of G8. Analysis of the latter transferase product by 13C- and 1H-nuclear magnetic resonance (NMR) spectroscopy shows it to be a branched molecule containing a beta-(1-3)-beta-(1-6)-branchpoint. It is suggested that the Mr 34,000 wall protein is a glucan branching enzyme, perhaps the key enzyme responsible for the transformation of the initial linear beta-(1-3)-glucan into the branched beta-(1-3)-beta-1-6)-glucan as found in the cell wall of C. albicans.
从白色念珠菌培养滤液中纯化内切 -（1,3）-β - 葡聚糖酶时，分离出一种分子量为34,000的壁蛋白作为副产物。纯化后的组分不含外切或内切β - 葡聚糖酶活性，十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳（SDS - PAGE）分析显示在分子量34,000处有一条蛋白带。用五个或更多葡萄糖基单元的海带寡糖孵育该蛋白组分的反应产物，通过凝胶过滤高效液相色谱（HPLC）分析，发现了一种独特的葡聚糖基转移酶活性。该酶特异性地从线性β -（1,3）- 葡聚糖的还原端切割出昆布二糖（G2），并将其余部分转移到另一种海带寡糖上。与昆布戊糖（G5）反应生成G2和在G8位置洗脱的产物。通过碳 - 13和氢 - 1核磁共振（NMR）光谱对后一种转移酶产物进行分析，表明它是一种含有β -（1,3）-β -（1,6）分支点的分支分子。有人提出，分子量为34,000的壁蛋白是一种葡聚糖分支酶，可能是负责将最初的线性β -（1,3）- 葡聚糖转化为白色念珠菌细胞壁中发现的分支β -（1,3）-β -（1,6）- 葡聚糖的关键酶。
