Synaptotagmin I’s Intrinsically Disordered Region Interacts with Synaptic Vesicle Lipids and Exerts Allosteric Control over C2A

Abstract

Synaptotagmin I (Syt I) is a vesicle-localized integral membrane protein that senses the calcium ion (Ca(2+)) influx to trigger fast synchronous release of neurotransmitter. How the cytosolic domains of Syt I allosterically communicate to propagate the Ca(2+) binding signal throughout the protein is not well understood. In particular, it is unclear whether the intrinsically disordered region (IDR) between Syt I's transmembrane helix and first C2 domain (C2A) plays an important role in allosteric modulation of Ca(2+) binding. Moreover, the structural propensity of this IDR with respect to membrane lipid composition is unknown. Using differential scanning and isothermal titration calorimetry, we found that inclusion of the IDR does indeed allosterically modulate Ca(2+) binding within the first C2 domain. Additionally through application of nuclear magnetic resonance, we found that Syt I's IDR interacts with membranes whose lipid composition mimics that of a synaptic vesicle. These findings not only indicate that Syt I's IDR plays a role in regulating Syt I's Ca(2+) sensing but also indicate the IDR is exquisitely sensitive to the underlying membrane lipids. The latter observation suggests the IDR is a key route for communication of lipid organization to the adjacent C2 domains.

The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis

“…Aside from the C2 domains, synaptotagmins exhibit substantial variation in amino acid sequence in the region between the transmembrane domain and the C2A domain. In Syt-1, the N- and C-terminal portions of this linker region are rich in basic and acidic residues, respectively, and have been suggested to comprise an electrostatic zipper that contributes to regulation of fusion pore opening and protein–lipid binding ( Lai et al, 2013 ; Lu et al, 2014 ; Fealey et al, 2016 ). The sequence of the canonical Syt-7 linker region displays a somewhat similar electrostatic pattern, although the overall sequence conservation is low ( Fig.…”

Structural Impact of Phosphorylation and Dielectric Constant Variation on Synaptotagmin’s IDR

“…The underlying mechanisms by which Syt 1 mediates this biological event remain incompletely understood. Our goal has been to investigate the allosteric network of Syt 1 to elucidate regulatory mechanisms that underlie controlled neurotransmitter release (2)(3)(4). Our group found that an intrinsically disordered region (IDR) within Syt 1 (residues $80-141) exerts allosteric influence over the adjacent C2 domain referred to as ''C2A'' ( Fig.…”

“…Our group found that an intrinsically disordered region (IDR) within Syt 1 (residues $80-141) exerts allosteric influence over the adjacent C2 domain referred to as ''C2A'' ( Fig. 1 A) (4). Until recently, this IDR had received little attention and its structural biology still represents a significant gap in our understanding of Syt 1 function.…”

Enhanced synaptotagmin plasticity derived from pairing intrinsic disorder with synaptic vesicle lipids

“…Recently, our group provided evidence in support of such a mechanism. 4 We found that the IDR of Syt-1 is structurally sensitive to the lipid composition of the membrane, undergoing pronounced changes upon association. While the IDR seems to be mostly disordered when associated with a membrane whose lipid composition mimics that of a synaptic vesicle, its interaction still has a profound impact on the adjacent C2 domain (C2A).…”