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Parallel Functional Changes in Independent Testis-Specific Duplicates of Aldehyde dehydrogenase in Drosophila

Parallel Functional Changes in Independent Testis-Specific Duplicates of Aldehyde dehydrogenase in Drosophila

Authors :
James D. Fry
Mahul Chakraborty
Source :
Molecular Biology and Evolution. 32:1029-1038
Publication Year :
2015
Publisher :
Oxford University Press (OUP), 2015.

Abstract

A large proportion of duplicates, originating from ubiquitously expressed genes, acquire testis-biased expression. Identifying the underlying cause of this observation requires determining whether the duplicates have altered functions relative to the parental genes. Typically, statistical methods are used to test for positive selection, signature of which in protein sequence of duplicates implies functional divergence. When assumptions are violat ed, however, such tests can lead to false inference of positive selection. More convincing evidence for naturally selected functional changes would be the occurrence of structural changes with similar functional consequences in independent duplicates of the same gene. We investigated two testis-specific duplicates of the broadly expressed enzyme gene Aldehyde dehydrogenase (Aldh )t hat arose in different Drosophila lineages. The duplicates show a typical pattern of accelerated amino acid substitutions relative to their broadly expressed paralogs, with statistical evidence for positive selection in both cases. Importantly, in both duplicates, width of the entrance to the substrate binding site, known a priori to influence substrate specificity, and otherwise conserved throughout the genus Drosophila, has been reduced, resulting in narrowing of the entrance. Protein structure modeling suggests that the reduction of the size of the enzyme’s substrate entry channel, which is likely to shift substrate specificity toward smaller aldehydes, is accounted for by the positively selected parallel substitutions in one duplicate but not the other. Evolution of the testis-specific duplicates was accompanied by reduction in expression of the ancestral Aldh in males, supporting the hypothesis that the duplicates may have helped resolve intralocus sexual conflict over Aldh function.

Details

ISSN :
15371719 and 07374038
Volume :
32
Database :
OpenAIRE
Journal :
Molecular Biology and Evolution
Accession number :
edsair.doi.dedup.....205b3c1ec00c12a406cfd87a6e9d51c2
Full Text :
https://doi.org/10.1093/molbev/msu407