Dnm1 forms spirals that are structurally tailored to fit mitochondria

Abstract

Dynamin-related proteins (DRPs) are large self-assembling GTPases whose common function is to regulate membrane dynamics in a variety of cellular processes. Dnm1, which is a yeast DRP (Drp1/Dlp1 in humans), is required for mitochondrial division, but its mechanism is unknown. We provide evidence that Dnm1 likely functions through self-assembly to drive the membrane constriction event that is associated with mitochondrial division. Two regulatory features of Dnm1 self-assembly were also identified. Dnm1 self-assembly proceeded through a rate-limiting nucleation step, and nucleotide hydrolysis by assembled Dnm1 structures was highly cooperative with respect to GTP. Dnm1 formed extended spirals, which possessed diameters greater than those of dynamin-1 spirals but whose sizes, remarkably, were equal to those of mitochondrial constriction sites in vivo. These data suggest that Dnm1 has evolved to form structures that fit the dimensions of mitochondria.

Chapter 13 Visualization of Dynamins

“…As observed with negative stain EM, a T-shape structure is seen at the lipid interface ( Fig. 6A; see insert); a common feature observed among all dynamin family members examined to date, regardless of differences in protein circumference (Ingerman et al, 2005;Kochs et al, 2005;Low and Lowe, 2006). When GTP is added to the dynamin tubes, a constriction in the helical structure occurs that changes the overall diameter of the helical array from 50 to 40 nm ( Fig.…”

“…2C) (Ingerman et al, 2005). These structures are much larger than dynamin spirals (~100 nm vs. ~50 nm).…”

“…1). Each domain is required for self-assembly of dynamins into functional, oligomeric structures (Ingerman et al, 2005;Ramachandran et al, 2006;Smirnova et al, 1999;Song et al, 2004). In addition to these conserved motifs, dynamins contain other functional domains specific to the cellular mechanism associated with each protein (Fig.…”

“…2). For dynamin and Dnm1, the oligomeric state is tailored to its function: dynamin forms structures with sizes comparable to the size of necks at budding vesicles (~50 nm) (Hinshaw and Schmid, 1995), while Dnm1 forms significantly larger structures required for mitochondrial fission with sizes comparable to diameters observed at mitochondrial constriction sites (~100 nm) (Ingerman et al, 2005). Furthermore, both Dnm1/Drp1 and MxA proteins have an apparent affinity for lipid despite lacking a PH domain.…”

The many shapes of mitochondrial death

“…Furthermore, overexpression of hFis1 results in fragmented mitochondria, whereas blocking hFis1 by microinjected antibodies or by short interfering RNA results in elongated and collapsed mitochondria (James et al, 2003;Yoon et al, 2003). The Drp-1 homologue in yeast, Dnm1, causes mitochondrial fragmentation by accumulating in foci at sites of mitochondrial division and elongating in spirals of Dnm1 oligomers that span the size of mitochondria and constrict the membranes, breaking down the tubular organelle (McNiven et al, 2000;Ingerman et al, 2005). Similarly, dynamin I oligomerizes at the neck of nascent plasma membrane endocytotic vesicles that are undergoing fission.…”