Intrinsic Disorder in α-Synuclein Regulates the Exocytotic Fusion Pore Transition

Abstract

Today, it is widely accepted that intrinsic disorder is strongly related to the cell cycle, during mitosis, differentiation, and apoptosis. Of particular interest are hybrid proteins possessing both structured and unstructured domains that are critical in human health and disease, such as α-synuclein. In this work, we describe how α-synuclein interacts with the nascent fusion pore as it evolves toward expansion. We unveil the key role played by its intrinsically disordered region as a thermodynamic regulator of the nucleation-expansion energy barrier. By analyzing a truncated variant of α-synuclein that lacks the disordered region, we find that the landscape of protein interactions with PIP2 and POPS lipids is highly altered, ultimately increasing the energy cost for the fusion pore to transit from nucleation to expansion. We conclude that the intrinsically disordered region in full-length α-synuclein recognizes and allocates pivotal protein:lipid interactions during membrane remodeling in the first stages of the fusion pore.

Myomerger Induces Membrane Hemifusion and Regulates Fusion Pore Expansion

“…For both systems, free energies decrease toward the metastable state at 0.4 < ξ e < 0.5. Although the free energy cost for fusion pore nucleation and expansion highly depends on the intermembrane separation, ,− the presence of 8 sMyomergers has the relative effect of lowering the nucleation–expansion free energy difference Δ G ne (ξ e ∼ 0 to ξ e ∼ 0.4) by ∼5 kJ/mol with respect to the membranes-only system. A similar result has already been reported for a pair of Synaptotagmin-1 C2B domains with direct consequences on the probability of kiss-and-run events , and for α-synuclein to describe the role played by its intrinsically disordered region. , …”

“…Leikina et al previously reported that Myomerger facilitates the formation of pores in cell membranes and liposomes. Here, we hypothesize that the introduction of sMyomergers in the extracellular space helps the bilayers to release free energy as the configurational change of the fusion pore from nucleation to expansion takes place . Therefore, the direct effect of sMyomergers is the gradual reduction of the nucleation–expansion free energy difference Δ G ne (ξ e ∼ 0 to ξ e ∼ 0.4).…”

“…Also, from a hemifusion stalk, variables ξ n and ξ e produce the required biases to sequentially nucleate the first fusion pore and later expand it. Again, ξ e has proven to be hysteresis-free and allows for useful free energy calculations 26,27,40 Therefore, we have started membrane fusion using variable ξ f , defined by eq 1 following previous developments and applications. 26,29,30,85 In 1 a spanning cylinder composed of N sf slices is filled with tail beads (C4A and C4B), 43 N sf (p) is the number of such beads within slice s inside the fusion cylinder, and δ sf is a continuous function in the interval [0 1] (δ sf = 0 for no beads in slice s and δ sf = 1 for 1 or more beads in slice s).…”

“…A similar result has already been reported for a pair of Synaptotagmin-1 C2B domains with direct consequences on the probability of kissand-run events 26,43 and for α-synuclein to describe the role played by its intrinsically disordered region. 40,44 sMyomergers Increase the Free Energy Cost to Expand the Fusion Pore. On top of favoring the formation of a hemifusion stalk and lowering the nucleation−expansion free energy difference (ΔG ne ), sMyomergers in the extracellular space have still another effect on the thermodynamics of the fusion pore.…”

Advancing Molecular Dynamics: Toward Standardization, Integration, and Data Accessibility in Structural Biology

“…Since their development in the 1970s, molecular dynamics-based approaches have significantly advanced and gained credibility as a tool for hypothesis testing, experimental motivation and interpretation, and enhancing our understanding of biology . These approaches, rooted in physical principles, are attractive for addressing various problems, including evaluating free energy differences, predicting structures, unraveling mechanisms of action, , and providing high-resolution descriptions of systems on a picosecond-by-picosecond basis, which cannot be achieved through experimental techniques alone.…”