Abstract：
Porphyran is a promising bioactive polysaccharide majorly composed of 4-linked α-l-galactopyranose-6-sulfate (L6S) and 3-linked β-d-galactopyranose (G) disaccharide repeating units. Carbohydrate-binding modules (CBMs) have been verified to be essential tools for investigating polysaccharides. However, no confirmed CBM binding to porphyran has been hitherto reported. In this study, an unknown domain with a predicted β-sandwich fold from a potential GH86 porphyranase was discovered, and further recombinantly expressed. The CBM protein (named FvCBM99) presented a desired specificity for porphyran tetrasaccharide with an affinity constant of 1.9 × 10-4 M, while it could not bind to agarose tetrasaccharide. The sequence novelty and well-defined function of FvCBM99 and its homologs reveal a new CBM family, CBM99. Besides, the application potential of FvCBM99 in in situ visualization of porphyran was demonstrated. The discovery of FvCBM99 provides a favorable tool for future studies of porphyran.
摘要：
卟啉是一种有前途的生物活性多糖，主要由4连接的α-1-吡喃半乳糖-6-硫酸酯（L6S）和3连接的β-d-吡喃半乳糖（G）二糖重复单元组成。碳水化合物结合模块（CBMs）已被证实是研究多糖的重要工具。然而,迄今尚无证实的CBM与卟啉结合的报道。在这项研究中,发现了一个未知的域，该域具有潜在的GH86卟啉酶的预测β-三明治折叠，并进一步重组表达。CBM蛋白（命名为FvCBMxx）对卟啉四糖具有所需的特异性，亲和常数为1.9×10-4M，而不能与琼脂糖四糖结合。FvCBMxx及其同源物的序列新颖性和明确的功能揭示了一个新的CBM家族。此外,证明了FvCBMxx在卟啉原位可视化中的应用潜力。FvCBMxx的发现为未来卟啉的研究提供了有利的工具。
