TITLE:
Characterization of the Intracellular Distribution of Adenine Nucleotide Translocase (ANT) in Drosophila Indirect Flight Muscles
AUTHORS:
Vivek K. Vishnudas, Shawna S. Guillemette, Panagiotis Lekkas, David W. Maughan, Jim O. Vigoreaux
KEYWORDS:
Drosophila; Insect Flight Muscle; Adenine Nucleotide Translocase; Phosphagen System
JOURNAL NAME:
CellBio,
Vol.2 No.3,
September
18,
2013
ABSTRACT:
Background: The high power output necessary for insect flight has driven the
evolution of muscles with large myofibrils (primary energy consumers) and
abundant mitochondria (primary energy suppliers). The intricate functional interrelationship
between these two organelles remains largely unknown despite its fundamental
importance in understanding insect flight bioenergetics. Unlike vertebrate
muscle that relies on a phosphagen (creatine phosphate/creatine kinase) system
to regulate high energy phosphate flux, insect flight muscle has been reported
to lack mitochondrial arginine kinase (analogous to creatine kinase), a key
enzyme that enables intracellular energy transport. Creatine kinase is known to
interact with mitochondrial adenine nucleotide translocase (ANT) in the
transfer of ADP and ATP into and out of the mitochondria. Results: Here, we use quantitative immunogold
transmission electron microscopy to show that in Drosophila melanogaster indirect flight muscles (IFM), ANT is present in the mitochondria as well as
throughout the myofibril. To confirm this unexpected result, we created a
transgenic line that expresses a chimeric GFP-ANT protein and used an anti-GFP
antibody to determine the intracellular distribution of the fusion protein in
the IFM. Similar to results obtained with anti-ANT, the fusion GFP-ANT protein
is detected in myofibrils and mitochondria. We confirmed the absence of
arginine kinase from IFM mitochondria and show that its sarcomeric (i.e., intramyofibrillar) distribution is
similar to that of ANT. Conclusions: These results raise the possibility that
direct channeling of nucleotides between mitochondria and myofibrils is
assisted by an ANT protein thereby circumventing the need for a phosphagen
shuttle in the IFM. The myofibrillar ANT may represent a unique adaptation in
the muscles that require efficient exchange of nucleotides between mitochondria
and myofibrils.