| Title: | A novel homodimeric geranyl diphosphate synthase from the orchid Phalaenopsis bellina lacking a DD(X)2-4D motif |
| Author(s): | Hsiao YY; Jeng MF; Tsai WC; Chuang YC; Li CY; Wu TS; Kuoh CS; Chen WH; Chen HH; |
| Address: | "Department of Life Sciences, National Cheng Kung University, Tainan 701, Taiwan" |
| DOI: | 10.1111/j.1365-313X.2008.03547.x |
| ISSN/ISBN: | 1365-313X (Electronic) 0960-7412 (Linking) |
| Abstract: | "Geranyl diphosphate (GDP) is the precursor of monoterpenes, which are the major floral scent compounds in Phalaenopsis bellina. The cDNA of P. bellina GDP synthase (PbGDPS) was cloned, and its sequence corresponds to the second Asp-rich motif (SARM), but not to any aspartate-rich (Asp-rich) motif. The recombinant PbGDPS enzyme exhibits dual prenyltransferase activity, producing both GDP and farnesyl diphosphate (FDP), and a yeast two-hybrid assay and gel filtration revealed that PbGDPS was able to form a homodimer. Spatial and temporal expression analyses showed that the expression of PbGDPS was flower specific, and that maximal PbGDPS expression was concomitant with maximal emission of monoterpenes on day 5 post-anthesis. Homology modelling of PbGDPS indicated that the Glu-rich motif might provide a binding site for Mg(2+) and catalyze the formation of prenyl products in a similar way to SARM. Replacement of the key Glu residues with alanine totally abolished enzyme activity, whereas their mutation to Asp resulted in a mutant with two-thirds of the activity of the wild-type protein. Phylogenetic analysis indicated that plant GDPS proteins formed four clades: members of both GDPS-a and GDPS-b clades contain Asp-rich motifs, and function as homodimers. In contrast, proteins in the GDPS-c and GDPS-d clades do not contain Asp-rich motifs, but although members of the GDPS-c clade function as heterodimers, PbGDPS, which is more closely related to the GDPS-c clade proteins than to GDPS-a and GDPS-b proteins, and is currently the sole member of the GDPS-d clade, functions as a homodimer" |
| Keywords: | "Amino Acid Sequence Cloning, Molecular DNA, Complementary/genetics DNA, Plant/genetics Dimethylallyltranstransferase/*genetics Flowers/enzymology/genetics Gene Expression Genes, Plant Models, Molecular Molecular Sequence Data Monoterpenes/metabolism Mutag;" |
| Notes: | "MedlineHsiao, Yu-Yun Jeng, Mei-Fen Tsai, Wen-Chieh Chuang, Yu-Chen Li, Chia-Ying Wu, Tian-Shung Kuoh, Chang-Sheng Chen, Wen-Huei Chen, Hong-Hwa eng Research Support, Non-U.S. Gov't England 2008/05/10 Plant J. 2008 Sep; 55(5):719-33. doi: 10.1111/j.1365-313X.2008.03547.x. Epub 2008 May 9" |
