Molecular cloning, structural analysis and mass spectrometric identification of native dioscorins of various yam species.
BACKGROUND
Dioscorins are the major storage proteins of yam tubers. However, the molecular nature of their heterogeneity in tubers has not been fully elucidated. In this study the authors isolated the dioscorin gene families of Dioscorea japonica and Dioscorea pseudojaponica, performed matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) and elucidated which dioscorin isoforms are the major constituents in tubers.


RESULTS
The dioscorin gene families of D. japonica (Dj-dioA1-Dj-dioA4, Dj-dioB1 and Dj-dioB2) and D. pseudojaponica (Dp-dioA1-Dp-dioA5 and Dp-dioB1) were cloned from cDNA libraries of yam tubers. The dioscorins isolated from Dioscorea alata (Da-dioscorins), D. japonica (Dj-dioscorins) and D. pseudojaponica (Dp-dioscorins) were mainly monomers, with a few dimers. The monomers contained one intramolecular disulfide bond (Cys(28)-Cys(187)) and belonged to Class A dioscorins with two cysteine residues. The dimers consisted of Class B dioscorins with one intermolecular disulfide bond (Cys(40)-Cys(40)). Results of MALDI-TOF-MS revealed that the Da-dioscorins were mainly encoded by Da-dioA2, Da-dioA3 and Da-dioA4. The majority of the Dj-dioscorins were encoded by Dj-dioA1, Dj-dioA2, Dj-dioA3 and Dj-dioB2. The Dp-dioscorins mainly comprised proteins encoded by Dp-dioA1, Dp-dioA3, Dp-dioA4, Dp-dioB1 and Dp-dioB2.


CONCLUSIONS
Determination of the constituents of dioscorin isoforms in yam tubers provides a basis for future studies of their physiological and biomedical functions.
Department of Life Science and Institute of Biotechnology, National Dong Hwa University, Hualien County 974, Taiwan.
Wei-Yi
WY
Tsai
Yi-Jyun
YJ
Jheng
Kuo-Hsuan
KH
Chen
Kuo-Wei
KW
Lin
Yen-Pen
YP
Ho
Ching-Chi
CC
Yang
Kuo-Chih
KC
Lin
D003001:Cloning, Molecular; D004032:Diet; D004044:Dietary Proteins / Q000032:analysis* / Q000302:isolation & purification; D027742:Dioscorea / Q000737:chemistry* / Q000235:genetics; D015723:Gene Library; D017343:Genes, Plant; D006801:Humans; D013058:Mass Spectrometry; D015394:Molecular Structure; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D035281:Plant Tubers / Q000737:chemistry*; D020033:Protein Isoforms; D013045:Species Specificity
D004044:Dietary Proteins; D010940:Plant Proteins; D020033:Protein Isoforms