The two subfamilies of rice glutelin differ in both primary and higher-order structures
Tomoyuki Katsube-Tanaka, Joy Bartolome A. Duldulao, Yuka Kimura, Shuichi Iida, Takeshi Yamaguchi, Junichi Nakano and Shigeru Utsumi
Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics Volume 1699, Issues 1-2 , 1 June 2004, Pages 95-102
2004
บทคัดย่อ
Rice glutelin, which accounts for 70–80% of the total proteins of the seeds, consists of two nutritionally different subfamilies (A and B types). Although the similarity in primary sequences between the two subfamilies is as high as 60%, we established conditions to discriminate the two subfamilies when low amounts of antigen are analyzed by immunoblot methods. The glutelin a polypeptides can be resolved into six bands labeled a1 to a6 by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Gel filtration analysis showed that glutelin exists as a polymerized and a smaller molecular weight form. Immunoblot analysis of SDS-PAGE resolved polypeptides showed that a2, a3, and a4 are an A type and that these A types as well as 1, a B type, are polymerized. The polymerization tendency clearly differed between the two subfamilies except for a1, which may be derived from GluB-4 as suggested by analysis using Escherichia coli expression systems of glutelin cDNA regions corresponding toa polypeptides. GluB-4 and all the A type subunits have an extra Cys residue in the hypervariable regions, corresponding to the C-terminal region of a polypeptide. Accordingly, the extra Cys residue is hypothesized to be responsible for the polymerization of glutelin.