Mutagenesis of the glucoamylase signal peptide of Saccharomyces diastaticus and functional analysis in Saccharomyces cerevisiae

To improve the efficiency of the glucoamylase signal peptide (GSP) of Saccharomyces diastaticus for the secretion of foreign proteins, hybrid plasmids containing one of four types of GSP mutant (m1, Pro(-18)-->Leu(-18); m2, Tyr(-13)-->Leu(-13); m3, Ser(-9)-->Leu(-9); m4, Asn(-5)-->Pro(-5)) were constructed and evaluated in Saccharomyces cerevisiae using Bacillus endo-1,4-beta-D-glucanase (CMCase) as a reporter gene. CMCase secretion by m1, m2 and m3 GSP mutants was increased, likely resulting from a higher probability of the modified GSP to assume an alpha-helical structure. Especially in the case of m3, the substitution of Leu for a polar residue, Ser(-9), in the hydrophobic region resulted in approximately a twofold increase in extracellular CMCase activity. In mutant 4, which disrupts the alpha-helix of GSP, CMCase was less efficiently secreted.