Mutations in DLD have been linked to severe metabolic disorders in humans, but it wasn't known that DLD was a moonlighting enzyme with two jobs: regulating metabolism and breaking down proteins.
The PNAS study describes how Mayo investigators identified DLD's role in reducing the amount of frataxin that is produced.
"These findings reveal a previously unrecognized mechanism by which certain DLD mutations can simultaneously induce the loss of a primary metabolic activity and the gain of a moonlighting proteolytic (breaking down enzymes) activity. The latter could contribute to the metabolic derangement associated with DLD deficiency and represent a target for therapies of this condition," the authors write.
Like all proteins, frataxin is continuously synthesized, and it carries out its function before it breaks down. Some proteins degrade more rapidly than others, but frataxin degrades at a much more rapid pace than other proteins. "We observed this degradation years ago and in doing so, we decided to go after the enzyme responsible for the degradation thinking it probably might play an important role in the regulation of frataxin and could represent a target therapy for Friedreich's ataxia," says Dr. Isaya.
The severity of Friedreich's ataxia is proportional to the decrease in the levels of frataxin: the lower the frataxin, the more severe the disease. "Yet, this correlation does not completely explain the clinical variability because even within the same family we may see individuals with different phenotypes -- one more severe than the other," Dr. Isaya says.
In Friedreich's ataxia, clinicians have long hypothesized the existence of gene modifiers -- genes that can influence the outcome of other gene mutations. "We believe that the enzyme we've identified is most likely a modifier of Friedreich's ataxia because mutations in that gene could increase