Biology subjects

Hristova, K.

Publications and source records attributed to Hristova, K..

3 recordsLinked to original sources

bioRxiv2021

Reversible blood-brain barrier opening utilizing the membrane active peptide melittin in vitro and in vivo

The blood-brain barrier (BBB) tightly controls entry of molecules and cells into the brain, restricting the delivery of therapeutics. Blood-brain barrier opening (BBBO) utilizes reversible disruption of cell-cell junctions between brain microvascular endothelial cells to enable transient entry into the brain. Development of BBBO techniques has been hindered by a lack of physiological models for in vitro study. Here, we utilize an in vitro tissue-engineered microvessel model to demonstrate that melittin, a membrane active peptide present in bee venom, supports BBBO. From endothelial and neuronal viability studies, we identify the accessible concentration range for BBBO. We then use a tissue-engineered model of the human BBB to optimize dosing and elucidate the mechanism of opening. Melittin and other membrane active variants transiently increase paracellular permeability via disruption of cell-cell junctions. In mice, we demonstrate a minimum clinically effective intra-arterial dose of 3 M{middle dot}min melittin, which is reversible within one day and neurologically safe. Melittin-induced BBBO represents a novel platform for delivery of therapeutics into the brain.

bioengineering↗

bioRxiv2021

Allosteric Regulation of the EphA2 Receptor Intracellular Region by Serine/Threonine Kinases

Eph receptor tyrosine kinases play a key role in cell-cell communication. However, lack of structural information on the entire multi-domain intracellular region of any Eph receptor has hindered detailed understanding of their signaling mechanisms. Here, we use an integrative structural biology approach combining X-ray crystallography, small-angle X-ray scattering and hydrogen-deuterium exchange mass spectrometry, to gain the first insights into the structure and dynamics of the entire EphA2 intracellular region. EphA2 promotes cancer malignancy through a poorly understood non-canonical form of signaling that depends on serine/threonine phosphorylation of the linker connecting the EphA2 kinase and SAM domains. We uncovered two distinct molecular mechanisms that may function in concert to mediate the effects of linker phosphorylation through an orchestrated allosteric regulatory network. The first involves a shift in the equilibrium between a "closed" configuration of the EphA2 intracellular region and an "open" more extended configuration induced by the accumulation of phosphorylation sites in the linker. This implies that cooperation of multiple serine/threonine kinase signaling networks is necessary to promote robust EphA2 non-canonical signaling. The second involves allosteric rearrangements in the kinase domain and juxtamembrane segment induced by phosphorylation of some linker residues, suggesting a link between EphA2 non-canonical signaling and canonical signaling through tyrosine phosphorylation. Given the key role of EphA2 in cancer malignancy, this new knowledge can inform therapeutic strategies.

biophysics↗

bioRxiv2020

Ligand-independent EGFR oligomers do not rely on the active state asymmetric kinase dimer

The human Epidermal Growth Factor Receptor (EGFR/ERBB1) is a Receptor Tyrosine Kinase (RTK) that forms active oligomers in response to ligand. Much evidence indicates that EGFR/ERBB1 forms oligomers in the absence of ligand, but the structure and physiological role of these ligand-independent dimers remain unclear. We use fluorescence microscopy to measure the oligomer stability and FRET efficiency for homo- and hetero-oligomers of fluorescent-protein labeled forms of EGFR and its paralog, Human Epidermal Growth Factor Receptor 2 (HER2/ERBB2) in vesicles derived from native cell membranes. Both receptors form ligand-independent oligomers at physiological plasma membrane concentrations. Mutations introduced in the EGFR kinase region at a key interface within the active state dimer alter the FRET efficiency within ligand-independent EGFR oligomers but do not affect their stability. These results indicate that ligand-independent EGFR oligomers do not require this interface and that the inactive state ensemble is distinct from the EGFR active state ensemble.

biophysics↗