Effects of point mutations on the thermostability of B. subtilis lipase: investigating nonadditivity.Molecular level understanding of mutational effects on stability and activity of enzymes is challenging particularly when several point mutations are incorporated during the directed evolution experiments.  Here, we report that the cumulative point mutations incorporated in mutants 2M (with two point mutations) to 6M (with six point mutations) possibly do not retain their original stabilizing nature in the most thermostable 12M mutant (with 12 point mutations).  Our analysis has revealed that reversal of certain point mutations in 12M had little effect on its conformational stability, suggesting that these mutations were probably inconsequential towards the thermostability of the 12M mutant. 
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