Globulin-P characteristics that promote its aggregation.

QUIROGA ALEJANDRA,; MARTINEZ NORA,; AÑON, MARÍA C

Bariloche

Congreso; XXXIX Anual meeting SAIB - SAB; 2003

Globulin-P, 11S-globulin and glutelin are the main protein fractions in Amaranth seeds. Although they are legumins, (oligomers with subunits composed of a 30 kD and a 20 kD disulfide linked polypeptide) they differ in their aggregation state: Globulin-P presents some peculiarities which make it a hallmark of amaranth. It revealed a strong trend towards polymerization and contains high amounts of a monomeric subunit of 56 kDa (P56). To obtain information about the structural characteristics that promote globulin-P aggregation, our objective was to compare conformational aspects of globulin-P and other legumins and to analyze the purified globulin-P polypeptides. Globulin-P, soybean and amaranth 11S-globulins, and gobulin-P polypeptides were purified and analyzed by electrophoresis, isoelectrofocusing, fluorescence spectroscopy and RP-HPLC. Fluorescence results suggested that the three globulins contained two kinds of tryptophan locations, one surrounded by non-polar elements and another close to the protein surface . Nevertheless, subtle differences were found. In the three legumins the 30 kDa polypeptides were the most acidic, but their pI ranges were different for each globulin. Five P56 subunits of different pI were found in globulin-P. These subunits showed the most hydrophobic character by RP-HPLC. The purified globulin-P polypeptides formed aggregates linked by disulfides. They showed high retention times in RP-HPLC. The presence of the hydrophobic P56 and the trend of its polypeptides to establish disulfide bridges may promote globulin-p polymerization. These polypeptide properties may not confer to globulin-P molecules very different conformational characteristics from other 11S-globulins.