Cheng Chiwai, Lim Boon L
Department of Zoology, University of Hong Kong, Pokfulam Road, Hong Kong, China.
Arch Microbiol. 2006 Mar;185(1):1-13. doi: 10.1007/s00203-005-0080-6. Epub 2006 Jan 10.
Phytate, which is one of the dominant organic phosphorus compounds in nature, is very stable in soils. Although a substantial amount of phytate is carried from terrestrial to aquatic systems, it is a minor component of organic phosphorus in coastal sediments. The ephemeral nature of phytate implies the rapid hydrolysis of phytate under aquatic conditions. Among the four classes of known phytases that have been identified in terrestrial organisms, only beta-propeller phytase-like sequences have been identified in the aquatic environment. A novel beta-propeller phytase gene (phyS), cloned from Shewanella oneidensis MR-1, was found to encode a protein with two beta-propeller phytase domains. The characterization of recombinant full-length PhyS and its domains demonstrated that Domain II was the catalytic domain responsible for phytate hydrolysis. The full-length PhyS displayed a K(m) of 83 microM with a kcat of 175.9 min(-1) and the Domain II displayed a K(m) of 474 microM with a kcat of 10.6 min(-1). These results confirm that the phyS gene encodes a functional beta-propeller phytase, which is expressed in S. oneidensis under phosphorus deficient condition. The presence of multiple sequences with a high similarity to phyS in aquatic environmental samples and the widespread occurrence of the Shewanella species in nature suggest that the beta-propeller phytase family is the major class of phytases in the aquatic environment, and that it may play an important role in the recycling of phosphorus.
植酸盐是自然界中主要的有机磷化合物之一，在土壤中非常稳定。尽管大量的植酸盐从陆地系统进入水生系统，但它在沿海沉积物中的有机磷中只占一小部分。植酸盐的短暂特性意味着它在水生条件下会迅速水解。在陆地生物中已鉴定出的四类已知植酸酶中，在水生环境中仅鉴定出了类β-螺旋桨植酸酶序列。从希瓦氏菌MR-1中克隆出的一个新的β-螺旋桨植酸酶基因（phyS），被发现编码一种含有两个β-螺旋桨植酸酶结构域的蛋白质。重组全长PhyS及其结构域的特性表明，结构域II是负责植酸盐水解的催化结构域。全长PhyS的米氏常数（K(m)）为83微摩尔，催化常数（kcat）为175.9分钟-1，结构域II的K(m)为474微摩尔，kcat为10.6分钟-1。这些结果证实，phyS基因编码一种功能性的β-螺旋桨植酸酶，它在缺磷条件下在希瓦氏菌中表达。在水生环境样本中存在多个与phyS高度相似的序列，以及希瓦氏菌在自然界中的广泛分布，表明β-螺旋桨植酸酶家族是水生环境中植酸酶的主要类别，并且它可能在磷的循环中发挥重要作用。
