I want to express STK4, and I've searched the paper for reference. When I check the protein kinase domain sequence for that kinase on Uniprot, it's 30-281, but the paper expresses the protein through a larger segment of the sequence (18-311). I know that the larger size of the protein is not good for expression, but is this because expressing just that domain makes it less stable or something? I can't see the full structure in Pdb, and I don't really understand why it would help with stability specifically.
As an additional question, most Pdb structures are listed as shorter sequences than the actual expressed ones, is this because they go through refinements and such to remove unimportant residues?
"I know that the larger size of the protein is not good for expression"
How do you know that it is the size of the protein that causes problems in expression? In my experience protein kinases are sometimes difficult to express especially when they are active and can cause toxic effects in E. coli through phosphorylation. Therefore, sometimes you see the cells dying upon induction or you get clones with inactive mutants of the protein because those are the only ones where the cells survive the presence of the kinase. Sometimes, this can happen even during sub-cloning without induced expression, just by leaky expression.
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