From Gene to Functional Protein Processing Steps in Plants

From Gene to Functional Protein Processing Steps in Plants 

In order to make molecular farming commercially profitable, recombinant proteins must be produced at a sufficiently high yield and in an active form. It has become clear that, for high-level protein accumulation, the stability of transgene expression can be as important as the expression level itself. The quantity of protein is determined by the rate of protein synthesis, assembly as well as proteolytic degradation [83]. 

Increased transcription levels are assumed to result in increased protein synthesis. One approach to reach this goal is to raise the transgene copy number by the use of amplification-promoting sequences derived from a spacer sequence of tobacco ribo-somal DNA [95]. Posttranscriptional processes such as capping, splicing and polya-denylation are important for high protein yields, and it is also important to maximize mRNA stability [84]. 

The folding of polypeptide chains and the assembly of multiple subunits are critical requirements when complex and multimeric proteins such as full size antibodies 

Expressing recombinant proteins as N-terminal fusions with ubiquitin [109] is another strategy that can help to achieve proper folding. Additionally, this is an elegant way to obtain proteins that do not start with a methionine residue, since the ubiquitin moiety is cleaved off by endogenous ubiquitin-specific proteases [100]. 

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