Heterogeneity of storage proteins in maize

Area of Science:

• Plant biochemistry
• Protein chemistry
• Maize genetics

Background:

• Zeins, the major storage proteins in maize (Zea mays L.) endosperm, exhibit significant charge heterogeneity.
• This heterogeneity is observed as approximately 15 bands in isoelectric focusing (IEF) within the pH range of 6-9.
• Previous studies indicated zeins are resistant to deamidation and contain minimal glycoprotein or lipoprotein components.

Purpose of the Study:

• To investigate the causes of extensive charge heterogeneity in maize zeins.
• To determine if extraction procedures or endosperm development influence zein heterogeneity.
• To elucidate the molecular basis of zein charge variations.

Main Methods:

• Isoelectric focusing (IEF) to separate zein components based on charge.
• Amino acid analysis of isolated zein fractions.
• Assessment of resistance to in vitro deamidation under various conditions.

Main Results:

• Zein heterogeneity in IEF is independent of extraction methods and endosperm development.
• Zeins are highly resistant to in vitro deamidation.
• Analysis suggests at least 90% of glutamic and aspartic acids are present as asparagine and glutamine, and heterogeneity arises from in vivo deamidation and gene mutations.

Conclusions:

• Maize zein heterogeneity is a complex phenomenon.
• It is attributed to both post-translational modifications (in vivo deamidation of asparagine/glutamine) and genetic variations (spot mutations).
• Extraction procedures and developmental stage do not account for the observed charge differences.