There has been great progress achieved with genetic engineering in improving
soybean protein quality. However, these improvements are not sufficient to
meet the nutritional requirements for food and feed. This recent study aimed
to increase soybean sulfur amino acid content by expressing the de novo Milk
Bundle protein MB-16, in transgenic soybean seed.

The MB-16 gene, originally developed for expression in rumen bacteria, was
introduced into the soybean (Glycine max (L.) Merrill) genome to improve its
seed nutritional quality. MB-16 codes for a de novo protein enriched in the
essential amino acids (EAA) methionine, threonine, lysine and leucine.
Constructs were designed using the soybean codon bias, with and without the
KDEL ER retention sequence.

Transformed events showed the same transcription pattern as those with the
soybean codon preference, but the transcript levels were lower at each
developmental stage. MB-16 protein levels were highest in full-sized green
seed, but virtually disappeared in mature seeds. However, amino acid
analysis of mature transgenic seeds showed a significant increase in
methionine and cysteine as compared to the parent. This indicates that MB-16
elevated the sulfur amino acids, improved the EAA seed profile and confirms
that a de novo synthetic gene can enhance the nutritional quality of
soybean.

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