Vesicle (biology and chemistry)

In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis), and the transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes (not to be confused with lysosomes). If there is only one phospholipid bilayer, the vesicles are called unilamellar liposomes; otherwise they are called multilamellar liposomes. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle. Vesicles perform a variety of functions. Because it is separated from the cytosol, the inside of the vesicl

Physiological regulation of the CDK16/PCTAIRE-1 protein kinase and its proposed role in the brain

Saifeldin Nasser Mohamed Ibrahim Shehata

Cell signalling, mediated to a large extent by protein kinase phosphorylation, plays a vital role in regulation of cellular function. PCTAIRE-1 (also known as cyclin-dependent protein kinase (CDK)16), is a Ser/Thr kinase that has been implicated in many cellular processes, including cell cycle, apoptosis, insulin secretion, spermatogenesis, neurite outgrowth, and vesicle trafficking. Most recently, it has been proposed as a novel X-linked intellectual disability (XLID) gene, where loss-of-function mutations have been found in patients. The precise molecular mechanisms that regulate PCTAIRE-1 remained largely obscure, and only few substrates have been proposed with no clear functional significance and physiological role. To understand the function of PCTAIRE-1, we previously utilised a peptide library screen to determine the consensus phosphorylation motif. We showed that PCTAIRE-1 preferentially phosphorylated peptide motifs that differed from the classical CDK family substrate preference, suggesting a more distinct role for the kinase. Furthermore, we showed that cyclin Y, a novel cyclin, robustly binds and activates PCTAIRE-1 > 100-fold. In this thesis, we have identified two phosphorylation sites on cyclin Y that are essential for binding the well-known adaptor protein 14-3-3, which we propose stabilizes cyclin Y in a favourable PCTAIRE-1-binding conformation. Mutation of these sites to non-phosphorylatable Ser residues abolished PCTAIRE-1 binding and activation. Furthermore, we have cloned human PCTAIRE-1 mutants identified in XLID patients, and confirmed their failure to bind the cyclin Y-14-3-3 activating complex. In order to understand the physiological relevance of PCTAIRE-1 activity, we have utilised a chemical genetics approach that exploits the ability of an engineered PCTAIRE-1 mutant to selectively modify its substrates, allowing them to be uniquely purified. We have identified three PCTAIRE-1 substrates (AAK1, dynamin 1 and synaptojanin 1) in mouse brain that regulate crucial steps of receptor endocytosis, namely receptor binding, vesicle scission and vesicle uncoating, which are all involved in the regulation of neuronal synaptic transmission. Collectively, this thesis work has provided key molecular regulatory mechanisms and potential downstream targets of PCTAIRE-1, which has laid the foundations for future studies of the role that PCTAIRE-1 plays in specific cellular functions and physiological and pathological settings.

EPFL2017

Neuronal Depolarization Drives Increased Dopamine Synaptic Vesicle Loading via VGLUT

Brian Donal McCabe

The ability of presynaptic dopamine terminals to tune neurotransmitter release to meet the demands of neuronal activity is critical to neurotransmission. Although vesicle content has been assumed to be static, in vitro data increasingly suggest that cell activity modulates vesicle content. Here, we use a coordinated genetic, pharmacological, and imaging approach in Drosophila to study the presynaptic machinery responsible for these vesicular processes in vivo. We show that cell depolarization increases synaptic vesicle dopamine content prior to release via vesicular hyperacidification. This depolarization-induced hyperacidification is mediated by the vesicular glutamate transporter (VGLUT). Remarkably, both depolarization-induced dopamine vesicle hyperacidification and its dependence on VGLUT2 are seen in ventral midbrain dopamine neurons in the mouse. Together, these data suggest that in response to depolarization, dopamine vesicles utilize a cascade of vesicular transporters to dynamically increase the vesicular pH gradient, thereby increasing dopamine vesicle content.

Cell Press2017

Insertion of Nanoparticle Clusters into Vesicle Bilayers

Davide Demurtas, Alke Fink, Rudolf Hovius

A major contemporary concern in developing eective liposomeÀnanoparticle hybrids is the present inclusion size limitation of nanoparticles between vesicle bilayers, which is considered to be around 6.5 nm in diameter. In this article, we present experimental observations backed by theoretical considerations which show that greater structures can be incorporated within vesicle membranes by promoting the clustering of nanoparticles before liposome formation. Cryo-transmission electron microscopy and cryo-electron tomography conrm these observations at unprecedented detail and underpin that the liposome membranes can accommodate exible structures of up to 60 nm in size. These results imply that this material is more versatile in terms of inclusion capabilities and consequently widens the opportunities in developing multivalent vesicles for nanobiotechnology applications.

Amer Chemical Soc2014

Physiological regulation of the CDK16/PCTAIRE-1 protein kinase and its proposed role in the brain

Saifeldin Nasser Mohamed Ibrahim Shehata

EPFL2017