In addition to the external factors mentioned above, the
sequence or structure of the target protein is also an important
determinant of its soluble expression level. An understanding of the
folding mechanism and the three-dimensional (3D) structure of the
heterologous protein in the host would enable solubility to be
enhanced by means of structure-guided mutagenesis [14]. In this
study, we investigated the relationship between the sequence of a
protein and its soluble expression level.
The a-amylase from Bacillus licheniformis (BLA) was selected to
be over-expressed in E. coli. Use of this protein has three advantages.
Firstly, the product of bla expression in E. coli was partly
soluble and a portion of the protein produced was incorporated
into cytoplasmic inclusion bodies. Secondly, BLA is an industrially
valuable enzyme [15]. Use of the mutation to enhance the soluble
expression of BLA would reduce the cost of production. Thirdly, the
3D structure of BLA (Fig. 1) has been resolved [16e18], which will
increase our understanding of the effect of the mutation on its
soluble expression in E. coli.