Single‐point mutations at the surface of MB‐1Trp lead to important changes in its conformational properties

Abstract

Protein design is currently used for the creation of new proteins with desirable traits. In our lab we focus on the synthesis of proteins with high essential amino acid content having potential applications in animal nutrition. One of the limitations we face in this endeavour is achieving stable proteins despite a highly biased amino acid content. We report here the synthesis and the characterization of three variants of MB-1Trp in which two solvent-exposed Leu have been replaced by Glu allowing for the formation of new salt bridges at the surface of the protein. Although both mutations were expected to be similar (i.e. same mutation in a comparable local environment), they appear to have different effects on MB-1Trp as shown by far-UV circular dichroism, thermal denaturation, fluorescence and proteolytic resistance measurements. For the mutation Leu68Glu, an increase in the protein melting temperature of 6 degrees C was observed. Surprisingly, the mutation in position Leu19Glu led to a decrease in melting temperature and a modification of tertiary structure.

Enhancement of essential amino acid contents in crops by genetic engineering and protein design

“…Further improvement of the folding and stability of the MB‐1 protein has been reported that should result in increased accumulation of the protein in the production host. Efforts to improve MB‐1 stability have considered several potential contributing factors: core packing (Gagnon et al ., 2000), helix ‘capping’ (Parker and Hefford, 1998), loop optimization (Simons et al ., 2001), addition of salt bridges (Sasseville et al ., 2004) and addition of disulphide bridges (Doucet et al ., 2002). Some of these projects have resulted in substantial improvement in the properties of MB‐1 as a potential nutritive protein.…”