Puroindolines: Impact of their presence on gluten forming proteins

Puroindolines (PINs) are wheat endosperm proteins that impact kernel texture. The expression of PINs is controlled by Pin-a and Pin-b genes located on the chromosome 5D (5DS). The occurrence of the wild type of both gene sequence results in soft endosperm whereas, the presence of only one functional gene or mutation results in hard endosperm. No information on the relationship between degree of grain hardness as impacted by different levels of PIN expression and gluten protein profile is available. Therefore, this study aimed at investigating the effect of PINs on protein content and profile in common wheat, Triticum. Aestivum L (Alpowa, soft wheat) and durum wheat, Triticum turgidum (Svevo) flours and their respective derivatives in which PIN genes were deleted (Hard Alpowa) or expressed (Soft Svevo). Protein content was determined following standard Dumas method. Molecular weight distribution of flour proteins was monitored by size exclusion High performance liquid chromatography (HPLC) with subsequent determination of molecular weight using mass spectrometry and protein characterization by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Gliadin/Glutenin ratio was calculated to determine the role of PINs in gliadin and glutenin expression and rearrangement. PINs expression resulted in a decrease in protein content (g/100g db) from 15.9% in Svevo to 14.8% in Soft Svevo. Similarly, 5DS distal end deletion resulted in an increase in protein content (g/100g db) from 12.2% in Alpowa to 14.8% in Hard Alpowa. Proteomics was useful in identifying the type of protein and its size and hence determining probable correlation between gluten forming proteins and PINs. When PINs were not present (Hard Alpowa and Svevo), the ratio high molecular weight polymeric proteins (glutenins) to gliadins was higher, and the opposite was true when PINs were present (Alpowa and soft Svevo). The present study highlighted a correlation between PINs and the profile of gluten forming proteins, which in turn may affect end-use quality. Further investigation on effect of changes in protein profile, and resulting end-use quality, as a function of PINs expression is warranted.