Mitochondria are the primary organelle involved in producing the bulk of cellular ATP and they are also involved in apoptosis and the mediation of several cellular signalling pathways. Mitochondria are highly dynamic organelles and undergo fission and fusion events that are vital for their function and cellular distribution. Mitochondrial dysfunction is suggested to be a key factor in various neurological diseases, and correct morphology has been identified as crucial in maintaining the high demands of ATP around synaptic connections in neurons. Our knowledge of the mechanisms which govern mitochondrial dynamics is in its infancy and even though several proteins have been identified as components of the dynamics machinery, structural information elucidation molecular interactions between the elements is missing. Recentlty two novel proteins have been identified to mediate mitochondrial fission, namely MiD49 and MiD51, which aid in the recruitment of the fission mediator dynamin-related protein 1 (Drp1) to the mitochondrial surface. The molecular function of MiD49/51 is not clear and the proteins lack obvious sequence motifs or domains. To gain new insights into the mechanism of action of these proteins, we determined the crystal structure of the cytosolic domain of human MiD51 to high resolution, using Xe-SAD. The protein displays a characteristic fold and following determination of both the apo form and protein co-crystallised with ligand, a nucleotide binding pocket was identified. The importance of key binding groove residues on the function of MiD51 is currently being investigated through mutagenesis approaches and co-crystallisation with other potential ligands. Structural comparison of MiD51 to other members of its class identified an additional loop as a unique feature in an otherwise highly conserved fold which we postulate to be key in the recruitment of Drp1. Removal of the loop alters Drp1 recruiting behaviour. These findings give a new dimension of insight into the function of MiD51 in Drp1 recruitment and open the possibility of a conserved protein fold having novel purpose.