Characterization of globulin and avenin protein profiles in oat (Avena sativa) using Osborne fractionation and novel genomic data

Abstract

Historically, cereal proteins are categorized in Osborne fractions based on their solubility: albumins (water-soluble), globulins (salt-soluble), prolamins (alcohol-soluble), and glutelins (soluble in dilute alkali solutions). In this work, sequentially extracted proteins were separated on a polyacrylamide gel and quantified using BCA assay. The SDS-PAGE protein patterns of different cereals and oat lines agree with their molecular weights reported elsewhere. Albumin appears to be the predominant protein in all cereals, which is not in line with previous findings – possibly due to presence of native interfering compounds. However, the relative globulin to avenin ratios agree with those reported so far – oat globulins are present in significantly higher amounts than avenins. Fertilization treatment revealed that globulin and glutelin are the fractions that increase the most upon application of nitrogen, while fertilization with nitrogen and sulphur has significant effect only on the glutelin fraction.
A total of 11 avenin genes were successfully annotated, which formed 3 distinct phylogenetic groups. All Belinda avenins are characterized by the presence of a peptide that is associated with celiac disease. Whereas, only one of the three subclasses was found to contain significantly high levels of sulfur-containing amino acids. The annotated globulins include 25 genes so far, but the annotation is not complete yet, and the gene family might be bigger than reported in this work. The globulins of Belinda were divided into 2 main groups that contain numerous smaller subclasses. The lysine content in Belinda globulins based on the amino acid sequence obtained from the genome is lower than the experimental values previously reported in the literature and the recommendations from FAO. More genomic studies are required to complete the globulin gene list, while the existing gene annotations need to be verified as functional genes.

Popular Abstract

Cereals constitute a large part of the daily diet around the world. Wheat, rice, and maize top other grains in terms of production and human consumption. Oat production is lower, and it is mostly used for animal feeding, but over the past few decades, its popularity and human consumption has been steadily increasing. Why? Oat has a well-balanced nutrient composition, and recent research states that it offers numerous health benefits when regularly consumed. What is more, the cultivation of oat requires fewer nutrients than other cereals. Thus, it can grow on nutrient-deficient soils and requires less fertilizer, making it a sustainable and inexpensive source of high-quality nutrients. Oat is a good source of vegetable-based proteins and hence can become a good alternative to meat and dairy products. Nowadays, there is a lot of research is conducted to characterize oat and improve its nutritional qualities even further.
Oat groat contains four types of proteins: albumins, globulins, avenins, and glutelins. Globulins are believed to have good amino acid composition compared to other cereal proteins due to the presence of high amounts of essential amino acids. They are believed to be the major protein found in oat and hence the main reason for its high-quality proteins. The results of this study contrast with those findings as oat albumins were found to be the main oat protein, while globulin is the second most abundant one. Although oat still contains relatively more globulins than other cereals. However, these discrepancies might be attributed to the presence of chemicals in albumin samples that disturb protein measurements. Avenins are believed to be the minor component in oat that is known for its poor nutritional qualities and toxicity in celiac disease patients. The results confirm that avenins are found in minimal amounts in oat, while wheat and barley contain a relatively higher amount of these gluten-like proteins.
It is essential to know how the protein composition of oat is affected by the availability of nutrients to select the right type and amounts of fertilizer. The fertilization of oat with nitrogen is known to raise its total protein content, and it is believed that globulin is the only protein fraction that increases. From this study, results conclude that both globulins and glutelins are the protein fractions that increase the most upon application of nitrogen, but there is also a significant relative increase in the amount of avenins. The effect of combined nitrogen and sulphur is not one-dimensional for all types of proteins in oat and does not follow the patterns observed for other cereals. Therefore, the impact of fertilization on oat protein quality needs to be further investigated as it is a very complex process with many factors that can affect the outcomes.
The availability of oats genetic code allows the analysis of proteins without stepping into the traditional laboratory. The amino acid composition, potential toxicity to celiac disease patients, and complex molecular mechanisms revolving around oat proteins can be now investigated and used to improve the quality of oat. The results based on the oat genome indicate that oat globulins contain less of the essential amino acids than stated in previous research. Whereas, several avenins are known to contain high levels of proline and amino acid patterns that might be associated with celiac disease. However, previous studies on the toxicity of these patterns reveal that oat avenins are less toxic than gluten and oats can be safely consumed by celiac disease patients.
The results that can be obtained both from the laboratory and from the genetic code of oat can allow scientists to improve the content and nutritional qualities of oat in the future. Furthermore, it can also enable more sustainable cultivation of oats with reduced amounts of fertilizers or pesticides

• author: Szewczyk, Mateusz
• supervisor: Olof Olsson; Lars Sjögren
• organization: Pure and Applied Biochemistry
• course: KBKM01 20201
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences; Technology and Engineering
• keywords: oats, cereal protein, nutrition, Osborne fractionation, genomics, avenin, globulin, celiac disease, fertilization, applied biochemistry, tillämpad biokemi
• language: English
• id: 9011921
• date added to LUP: 2020-06-12 16:37:22
• date last changed: 2020-06-12 16:37:22