# Structural and functional characterization of the brain-specific dynamin superfamily member RNF112

## TL;DR

This study reveals the structure and function of RNF112, a brain-specific dynamin-like protein, showing how it uses GTP to reshape membranes and offering insights into its role in cellular processes.

## Contribution

The paper presents the first crystal structures of RNF112 and demonstrates its GTP-dependent membrane remodeling activity.

## Key findings

- RNF112 undergoes domain rearrangement during GTP hydrolysis, transitioning from a self-restraint to a dimeric conformation.
- Engineered RNF112 can mediate membrane remodeling in a GTP-dependent manner when localized to the endoplasmic reticulum.
- Key residues for RNF112's mechanochemical activity were identified through structural and biochemical analysis.

## Abstract

The dynamin superfamily GTPases are key membrane remodelers in cells. As a recently identified member, RNF112 is essential for functional synapses by regulating endosome and mitochondrial morphology, but its mechanisms remain obscure. This study reports the crystal structures of modified RNF112 in different stages of GTP hydrolysis and reveals its unique feature in GTP hydrolysis-coupled domain rearrangement. Based on the structural information, the biochemical properties of RNF112 as a mechanochemical enzyme were systematically investigated and the key residues for its activity were identified. Finally, engineered RNF112 is capable of mediating membrane remodeling in a GTP-dependent manner. These results pave the way for further research characterizing RNF112-related diseases and broaden our understanding of dynamin superfamily.

Most members of the dynamin superfamily of large guanosine triphophatases (GTPases) have an ability to remodel membranes in response to guanosine triphosphate (GTP) hydrolysis. Ring Finger Protein 112 (RNF112) (ZNF179/neurolastin) is a recently identified brain-specific dynamin-like protein possessing a really interesting new gene (RING) finger domain. Despite its essential role as an E3 ligase in neuron development, the architecture of RNF112 and the exact role of its GTPase activity remain unknown. Here, we determined the crystal structure of truncated RNF112 (RNF112T) containing a GTPase domain (GD) and three-helical middle domain (MD) at different nucleotide-loading states. In the nucleotide-free (apo) state, the monomeric RNF112T remained in a unique self-restraint conformation characterized by docking of the proximal end of the MD to a groove in the GD. At the transition state of GTP hydrolysis, the MD was released from the GD and stretched aside to form an intertwined RNF112T homodimer. Engineered RNF112 equipped with the C-terminal elements of ATL1 or the two transmembrane domains of yeast Sac1p relocated to the endoplasmic reticulum and was capable of mediating membrane remodeling. Taken together, our results offer necessary understandings of RNF112 as a dynamin-like large GTPase in its cellular function and provide insights into the functional mechanisms of dynamin superfamily proteins.