Differential Regulation of Dynamin-related Protein 1 Splice Variants by Membrane Adaptors

We begin the first biochemical examination of the multiple splice variants of human Dynamin-related protein 1 (Drp1), a GTPase involved in mitochondrial fission. While eight such variants, generated through alternative mRNA splicing, have been identified, here we focus on two: the shortest variant (Short) which is ubiquitous, and the longest (Long), which piqued our interest since Drp1 Long is expressed exclusively in neurons. We now establish the various functional differences between these two Drp1 splice variants. Our data reveal that whereas Drp1 Short exhibits constitutively high GTPase activity, Drp1 Long does not. Interestingly, mitochondrial outer membrane proteins, mitochondrial fission protein 1 (Fis1) and mitochondrial fission factor (Mff) that putatively function as receptors for Drp1 differentially regulate the enzymatic activity of the two splice variants. It is possible that the roles of Mff and Fis1, which have conflicting reports in the literature, may vary across Drp1 splice variants and thus be tissue specific. To gain a better understanding of the role of such Drp1 effectors, we focus primarily on Mff, as it has the strongest observed effect on Drp1 enzymatic activity, and probe its mechanism of action using a variety of biochemical and biophysical tools