藻类磷酸甘露糖异构酶基因的序列结构特点及系统进化分析

STRUCTURAL FEATURE AND PHYLOGENETIC ANALYSIS OF PHOSPHOMANNOSE ISOMERASE GENE IN ALGAE

磷酸甘露糖异构酶基因(phosphomannose isomerase,PMI)编码磷酸甘露糖异构酶(PMI),可逆催化甘露糖-6-磷酸和果糖-6-磷酸之间的相互转化,在GDP-D-甘露糖的合成中起重要的作用,后者是生物体合成糖蛋白和糖脂必需的前体物质。本文根据在Genbank中已经登录的部分藻类PMI基因序列,与部分细菌、真菌、植物和动物的PMI基因序列做比较,研究其进化趋势和规律及其基因结构,为以后在大型藻类中研究该基因奠定基础。系统进化分析表明,藻类的PMI基因有2个进化方向,绿藻类的PMI基因与高等植物的进化趋势一致;而杂色藻类(硅藻和褐藻)则单独形成一个进化分支。多序列比对表明,磷酸甘露糖异构酶蛋白有3个保守区,其中有4个氨基酸残基位点是金属离子结合位点,分别为2个Glu和2个His。对部分藻类的PMI基因进行结构分析表明:在比较低等的藻类中,PMI基因没有内含子插入,而较高等的藻类中则有不同数目和长度的内含子插入。对部分藻类PMI基因的生物信息学分析结果显示,PMI基因编码的蛋白为酸性蛋白,分子量在40到60kDa之间;二级结构中均以α-螺旋和无规则卷曲为主;三级结构与二级结构相吻合。

Phosphomannose isomerase catalyze reversible isomerization between D-fructose-6-phosphate and D-mannose-6-phosphate and plays an important role in the biosynthesis of GDP-D-mannose which is a required precursor of glycoproteins and glycolipids. In order to study the phylogeny relationship and gene structures of PMI, gene sequences of algae were analyzed with a combination of other species which were registered on the Genbank. Phylogenetic analysis showed that there are two evolutionary directions of algae PMI genes. Green alga were close with green plant while variegated alga formed a single evolutionary direction. The result of multiple sequence alignment showed that there were three conserved regions in algae PMIs and four amino acid residues sites （two glutamic acids and two histidines） participating in metal-binding. The structure analysis showed nonexistence of intron in relatively lower alga but different numbers and length of introns in the higher alga. Then the PMI gene sequences were analyzed by bioinformatics tools. The results showed that all encoded PMI proteins were acidic with the molecular weight ranging from 40 to 60 kDa. The main proteins secondary structure motifs were α-helix and random coil, and the tertiary structures were consistent with the secondary structure.