Ekborg Nathan A, Taylor Larry E, Longmire Atkinson G, Henrissat Bernard, Weiner Ronald M, Hutcheson Steven W
Department of Cell Biology and Molecular Genetics, Microbiology Building, University of Maryland, College Park, MD 20742, USA.
Appl Environ Microbiol. 2006 May;72(5):3396-405. doi: 10.1128/AEM.72.5.3396-3405.2006.
Saccharophagus degradans 2-40 (formerly Microbulbifer degradans 2-40) is a marine gamma-subgroup proteobacterium capable of degrading many complex polysaccharides, such as agar. While several agarolytic systems have been characterized biochemically, the genetics of agarolytic systems have been only partially determined. By use of genomic, proteomic, and genetic approaches, the components of the S. degradans 2-40 agarolytic system were identified. Five agarases were identified in the S. degradans 2-40 genome. Aga50A and Aga50D include GH50 domains. Aga86C and Aga86E contain GH86 domains, whereas Aga16B carries a GH16 domain. Novel family 6 carbohydrate binding modules (CBM6) were identified in Aga16B and Aga86E. Aga86C has an amino-terminal acylation site, suggesting that it is surface associated. Aga16B, Aga86C, and Aga86E were detected by mass spectrometry in agarolytic fractions obtained from culture filtrates of agar-grown cells. Deletion analysis revealed that aga50A and aga86E were essential for the metabolism of agarose. Aga16B was shown to endolytically degrade agarose to release neoagarotetraose, similarly to a beta-agarase I, whereas Aga86E was demonstrated to exolytically degrade agarose to form neoagarobiose. The agarolytic system of S. degradans 2-40 is thus predicted to be composed of a secreted endo-acting GH16-dependent depolymerase, a surface-associated GH50-dependent depolymerase, an exo-acting GH86-dependent agarase, and an alpha-neoagarobiose hydrolase to release galactose from agarose.
嗜糖降解菌2-40（原称降解微球菌2-40）是一种海洋γ-亚群变形菌，能够降解多种复杂多糖，如琼脂。虽然几种琼脂分解系统已通过生化方法进行了表征，但琼脂分解系统的遗传学仅得到部分确定。通过使用基因组学、蛋白质组学和遗传学方法，确定了嗜糖降解菌2-40琼脂分解系统的组成成分。在嗜糖降解菌2-40基因组中鉴定出了五种琼脂酶。Aga50A和Aga50D包含GH50结构域。Aga86C和Aga86E含有GH86结构域，而Aga16B带有GH16结构域。在Aga16B和Aga86E中鉴定出了新的6型碳水化合物结合模块（CBM6）。Aga86C有一个氨基末端酰化位点，表明它与表面相关。通过质谱在从琼脂培养细胞的培养滤液中获得的琼脂分解组分中检测到了Aga16B、Aga86C和Aga86E。缺失分析表明，aga50A和aga86E对琼脂糖的代谢至关重要。结果表明，Aga16B能内切降解琼脂糖以释放新琼脂四糖，类似于β-琼脂酶I，而Aga86E被证明能外切降解琼脂糖以形成新琼脂二糖。因此，预计嗜糖降解菌2-40的琼脂分解系统由一种分泌型内切作用的GH16依赖性解聚酶、一种表面相关的GH50依赖性解聚酶、一种外切作用的GH86依赖性琼脂酶和一种α-新琼脂二糖水解酶组成，后者可从琼脂糖中释放半乳糖。
