Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Poster Abstracts

49-POS Board 49 DIGGING INTO THE MOLECULAR DEGREES OF FREEDOM LEADING TO DYNAMIN MEDIATED MEMBRANE FISSION: INSIGHTS FROM MULTISCALE MOLECULAR MODELING ON THE "CATALYTIC" ROLE OF PLECKSTRIN HOMOLOGY DOMAIN Kirtika Jha 1 ; Krishnakanth Baratam 1 ; Vikas Dubey 1 ; Thomas J Pucadyil 2 ; Anand Srivastava 1 ; 1 Indian Institute of Science-Bangalore, Molecular Biophysics Unit, Bangalore, Karnataka, India 2 Indian Institute of Science Education and Research- Pune, Biological Sciences, Pune, Maharashtra, India Classical dynamin associates with the plasma membrane localized phosphatidylinositol-4,5- bisphosphate through the centrally located pleckstrin homology domain (dyn1-PHD). Dyn1-PHD is known to be a dispensable domain as dynamin-mediated fission can take place without it as is the case with extant bacterial and mitochondrial dynamins. Interestingly however, recent reconstitution experiments show that the rate of membrane fission slows down manifold when dyn1-PHD is replaced with polyhistidine or polylysine linker in a way that doesn’t compromise the scaffold fidelity. These observations suggest that dyn1-PHD may be ‘expediting’ the fission reaction in certain ways during synaptic vesicle recycling. In this work, we have used a multiscale modeling approach by combining together atomistic molecular dynamics simulations, mixed-resolution membrane mimetic models, coarse-grained molecular simulations and free- energy advanced sampling (metadynamics) methods to explore the molecular basis of the dyn1- PHD interactions with the membrane. We report the molecular-level insights into the possible role of dyn1-PHD as ‘catalyst’ and show that: (i) dyn1-PHDs make the membrane more pliable for fission and also modulate the lipids towards conformations that favor hemi-fission states. (ii) dyn1-PHD associates with membrane in multiple orientations using variable loops as the pivoting motifs. We explain our observations against the recently published Cryo-EM data of the dynamin collar on membrane and propose an “ orientation selection ” design principle behind the flexibility of dyn1-PHD, a possible result of the severe demands on the reconfigurations that dynamin collar needs to undergo during the fission cycle. (iii) Lastly, we identify key residues that stabilize the inositol-PHD interactions and suggest mutations that can restrict the ability of the dyn1-PHD to associate with membrane in multiple orientations. Together, these observations provide a molecular-level understanding of the catalytic role of the PHD in dynamin-mediated membrane fission.

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