The molecular ecology of biological invasions: what do we know about non-additive genotypic effects and invasion success?

Recent research suggests that non-additive genotypic effects may play an important role in the establishment success of invasive species. However, most empirical data for these inferences come from greenhouse experiments. Only recently has researchers tested non-additive genotypic effects and establishment success of invasive alien species under field conditions. Here we give a brief overview of this research and also carefully consider data from the first publication, to our knowledge, to report on non-additive genotypic effects on invasion success under field conditions. We identify some shortcomings in this important study and make suggestions for future research aimed at better understanding the contributions of non-additive genotypic effects to establishment success and invasion.     

Stability and unfolding of reduced Escherichia coli glutaredoxin 2: a monomeric structural homologue of the glutathione transferase family

Glutaredoxin 2 (Grx2) from Escherichia coli is monomeric and an atypical glutaredoxin that takes part in the monothiol deglutathionylation of proteins. Unlike its orthologs, Grx2 is a larger molecule with a canonical glutathione transferase (GST) fold that consists of two structurally distinct domains, an N-terminal glutaredoxin domain and a C-terminal alpha-helical domain. While GSTs are dimeric proteins, the conformational stability and unfolding kinetics of Grx2 were investigated to establish the contribution made by the domain interface to the stability of the tertiary structure of GST-like proteins without any influence from quaternary interactions. Equilibrium unfolding transitions for Grx2, using urea as a denaturant, are monophasic and exhibit coincidence of the fluorescence and CD data indicative of a concerted loss or formation of tertiary and secondary structure. The data fit well to a two-state N <--> U model with no evidence that an intermediate is being formed. The experimental m value [2.7 kcal mol (-1) (M urea) (-1)] is in excellent agreement with a predicted value of 2.5 kcal mol (-1) (M urea) (-1) based on the amount of surface area expected to become exposed during unfolding. These findings provide evidence that the two structurally distinct domains of Grx2 behave as a single cooperative folding unit. The unfolding kinetics are complex which, as a result of native-state heterogeneity, are characterized by two observable unfolding reactions that occur in parallel. A major population representing one distinct nativelike form unfolds on a fast track to denatured Grx2 with cis-Pro49. This is followed by a spectroscopically silent cis-trans proline isomerization reaction as determined by interrupted unfolding experiments. A minor population representing the other distinct nativelike form unfolds slowly with its rate being limited by an undetermined structural isomerization reaction. Further, there is no evidence indicating that unfolding proceeds via a high-energy intermediate that might suggest independent unfolding of the two nonidentical domains in Grx2. The kinetics data are, therefore, consistent with the existence of cooperativity between the domains, in agreement with the equilibrium data.