Deciphering the distribution of starch granule-associated proteins within maize and potato starch granules by...

Distribution and types of starch granule-associated proteins (SGAPs) in two typical starches (cereal maize starch and tuber potato starch) were investigated by sequential α-amylase hydrolysis. For maize starch, hydrolysis progressively advanced from the internal hilum region toward the granule periphery, accompanied by increased SGAPs content after 24 h hydrolysis, indicating higher SGAPs abundance in the granule periphery than in the hilum. Granule-bound starch synthase (GBSS) was the dominant protein throughout hydrolysis. Fourteen unique proteins detected only in native maize starch but undetectable after hydrolysis were involved in glycolytic flux, amino acid/nitrogen metabolism, nitrogen reserves and protein maturation, suggesting these proteins may be localized in the internal hilum. For potato starch, GBSS was also identified as the dominant protein and exhibited a concentric ring distribution within granules. Small granules (3-10 μm) were almost completely hydrolyzed after 24 h, whereas large granules were only affected on the surface. Comparative of SGAPs composition between native and 24 h hydrolyzed potato starches revealed that small granules contained more soluble starch synthase (SSS) and GBSS but less α-glucan water dikinase (GWD) than large granules. This study provides new insights into the composition and spatial heterogeneity of SGAPs within starch granules.