Abstract
BackgroundAll known attempts to isolate and characterize mammalian class V alcohol dehydrogenase (class V ADH), a member of the large ADH protein family, at the protein level have failed. This indicates that the class V ADH protein is not stable in a non-cellular environment, which is in contrast to all other human ADH enzymes. In this report we present evidence, supported with results from computational analyses performed in combination with earlier in vitro studies, why this ADH behaves in an atypical way.ResultsUsing a combination of structural calculations and sequence analyses, we were able to identify local structural differences between human class V ADH and other human ADHs, including an elongated β-strands and a labile α-helix at the subunit interface region of each chain that probably disturb it. Several amino acid residues are strictly conserved in class I–IV, but altered in class V ADH. This includes a for class V ADH unique and conserved Lys51, a position directly involved in the catalytic mechanism in other ADHs, and nine other class V ADH-specific residues.ConclusionsIn this study we show that there are pronounced structural changes in class V ADH as compared to other ADH enzymes. Furthermore, there is an evolutionary pressure among the mammalian class V ADHs, which for most proteins indicate that they fulfill a physiological function. We assume that class V ADH is expressed, but unable to form active dimers in a non-cellular environment, and is an atypical mammalian ADH. This is compatible with previous experimental characterization and present structural modelling. It can be considered the odd sibling of the ADH protein family and so far seems to be a pseudoenzyme with another hitherto unknown physiological function.Electronic supplementary materialThe online version of this article (doi:10.1186/s12858-016-0072-y) contains supplementary material, which is available to authorized users.
Highlights
IntroductionAll known attempts to isolate and characterize mammalian class V alcohol dehydrogenase (class V Alcohol dehydrogenase (ADH)), a member of the large ADH protein family, at the protein level have failed
All known attempts to isolate and characterize mammalian class V alcohol dehydrogenase, a member of the large Alcohol dehydrogenase (ADH) protein family, at the protein level have failed
It was observed that the class V ADH model formed elongated β-strands, one β-strand in each chain, in the region involved in dimer interaction
Summary
All known attempts to isolate and characterize mammalian class V alcohol dehydrogenase (class V ADH), a member of the large ADH protein family, at the protein level have failed. This indicates that the class V ADH protein is not stable in a non-cellular environment, which is in contrast to all other human ADH enzymes. Mammalian class I–IV have been characterized extensively at DNA and protein levels where the common trait is the ability to act as a general alcohol metabolizing enzyme with NAD+ as electron acceptor. All mammalian class I–IV ADH enzymes act as dimers, where each subunit contains two zinc atoms, one catalytic and one structural. The structural zinc is located in a loop at the edge of the enzyme where it is coordinated by four Cys and has been shown to be crucial for the structure and dimer formation [4, 6]
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