VDAC/porin is present in sarcoplasmic reticulum from skeletal muscle

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Abstract
In this study we demonstrate the existence of a protein with properties of the voltage-dependent anion channel (VDAC) in the sarcoplasmic reticulum (SR) using multiple approaches as summarized in the following: (a) 35 and 30 kDa proteins in different SR preparations, purified from other membranal systems by Ca2+/oxalate loading and sedimentation through 55% sucrose, cross-react with four different VDAC monoclonal antibodies. (b) Amino acid sequences of three peptides derived from the SR 35 kDa protein are identical to the sequences present in VDAC1 isoform. (c) Similar to the mitochondrial VDAC, the SR protein is specifically labeled by [14C]DCCD. (d) Using a new method, a 35 kDa protein has been purified from SR and mitochondria with a higher yield for the SR. (e) Upon reconstitution into a planar lipid bilayer, the purified SR protein shows voltage-dependent channel activity with properties similar to those of the purified mitochondrial VDAC or VDAC1/porin 31HL from human B lymphocytes, and its channel activity is completely inhibited by the anion transport inhibitor DIDS and about 80% by DCCD. We also demonstrate the translocation of ATP into the SR lumen and the phosphorylation of the luminal protein sarcalumenin by this ATP. Both ATP translocation and sarcalumenin phosphorylation are inhibited by DIDS, but not by atractyloside, a blocker of the ATP/ADP exchanger. These results indicate the existence of VDAC, thought to be located exclusively in mitochondria, in the SR of skeletal muscle, and its possible involvement in ATP transport. Together with recent studies on VDAC multicompartment location and its dynamic association with enzymes and channels, our findings suggest that VDAC deserves attention and consideration as a protein contributing to various cellular functions.

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