Biomedical subjects

B Davletov

Publications and source records attributed to B Davletov.

6 recordsLinked to original sources

PubMed2006

SNAP25 is a pre-synaptic target for the depressant action of reactive oxygen species on transmitter release.

Reactive oxygen species (ROS) participate in various physiological and pathological processes in the nervous system, but the specific pathways that mediate ROS signalling remain largely unknown. Using electrophysiological techniques and biochemical evaluation of isolated fusion proteins, we explored the sensitivity to standard oxidative stress of the entire synapse, the pre-synaptic machinery and essential fusion proteins underlying transmitter exocytosis. Oxidative stress induced by H(2)O(2) plus Fe(2+) inhibited both evoked and spontaneous quantal release from frog or mouse motor nerve endings, while it left post-synaptic sensitivity unchanged. The depressant effect of H(2)O(2) on acetylcholine release was pertussis toxin-insensitive, ruling out G-protein cascades. Experiments with ionomycin, a Ca(2+) ionophore, revealed that ROS directly impaired the function of releasing machinery. In line with this, SNAP25, one of three essential fusion proteins, showed a selectively high sensitivity to the oxidative signals. Several ROS scavengers enhanced evoked synaptic transmission, consistent with tonic inhibition by endogenous ROS. Our data suggest that ROS-induced impairment of releasing machinery is mediated by SNAP25, which appears to be a pre-synaptic ROS sensor. This mechanism of ROS signalling could have widespread implications in the nervous system and might contribute to the pathogenesis of neurodegenerative diseases.

Animals↗

PubMed2001

Non-invasive detection of apoptosis using magnetic resonance imaging and a targeted contrast agent.

The C2 domain of synaptotagmin I, which binds to anionic phospholipids in cell membranes, was shown to bind to the plasma membrane of apoptotic cells by both flow cytometry and confocal microscopy. Conjugation of the protein to superparamagnetic iron oxide nanoparticles allowed detection of this binding using magnetic resonance imaging. Detection of apoptotic cells, using this novel contrast agent, was demonstrated both in vitro, with isolated apoptotic tumor cells, and in vivo, in a tumor treated with chemotherapeutic drugs.

Animals↗

PubMed1998

Calcium-dependent membrane penetration is a hallmark of the C2 domain of cytosolic phospholipase A2 whereas the C2A domain of synaptotagmin binds membranes electrostatically.

C2 domains have been identified in a wide range of intracellular proteins, including lipid modifying enzymes, protein kinases, GTPases, and proteins involved in membrane trafficking. Many C2 domains bind membranes in a calcium-dependent manner. The first C2 domain from synaptotagmin I (SytIC2A) and the C2 domain from cytosolic phospholipase A2 (cPLA2C2) are among the best characterized C2 domains in terms of their structures and calcium binding. Here we demonstrate that the protein-lipid interaction is dramatically different for these two domains. Photolabeling with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID) in the presence of phospholipid vesicles indicates that cPLA2C2 penetrates into the hydrophobic region of the membrane. Hydrophobic surfaces on cPLA2C2 are exposed even in the absence of calcium, but only in its presence does the domain penetrate into the nonpolar core of the membrane. The interaction of SytIC2A with phospholipid membranes is primarily electrostatic with binding being abolished in 500 mM NaCl. Because soluble phospholipid head group analogues do not compete with binding of either SytIC2A or cPLA2C2 to vesicles, it is likely that membrane binding by these domains involves multiple interactions.

Animals↗

PubMed1993

Phosphorylation of synaptotagmin I by casein kinase II.

Synaptotagmin I is an abundant synaptic vesicle protein that binds Ca2+ in a phospholipid-dependent manner and is thought to function in synaptic vesicle exocytosis. We have now studied the phosphorylation of synaptotagmin I. Synaptotagmin I is one of the major substrates in brain for casein kinase II, which phosphorylates synaptotagmin at a single threonine. The phosphorylation site was mapped using recombinant proteins to threonine 128 of synaptotagmin I, which is located in the sequence between the transmembrane region and the C2 domain repeats of synaptotagmin I. The phosphorylation site of synaptotagmin I is also present in synaptotagmin II and is evolutionarily conserved between different species. Preceding the phosphorylation site, synaptotagmins I and II contain a lysine-rich sequence. Casein kinase II phosphorylation of many substrates is strongly stimulated by the addition of polylysine, but phosphorylation of synaptotagmin I by casein kinase II is not. In recombinant proteins, removal of the lysine-rich sequence of synaptotagmin I makes its phosphorylation dependent on exogenous polylysine, suggesting that the lysine-rich sequence in synaptotagmin serves as an endogenous polylysine stimulation signal for casein kinase II. Our data demonstrate that synaptotagmin I is an efficient substrate for casein kinase II at a conserved site with a possible modulatory role in nerve terminal function.

Amino Acid Sequence↗

PubMed1993

Interaction of synaptotagmin with the cytoplasmic domains of neurexins.

Synaptotagmin, a major intrinsic membrane protein of synaptic vesicles that binds Ca2+, was purified from bovine brain and immobilized onto Sepharose 4B. Affinity chromatography of brain membrane proteins on immobilized synaptotagmin revealed binding of alpha- and beta-neurexins to synaptotagmin in a Ca(2+)-independent manner. Using a series of recombinant proteins in which glutathione S-transferase was fused to the cytoplasmic domains of three different neurexins or of control proteins, it was found that synaptotagmin specifically interacts with the cytoplasmic domains of neurexins but not of control proteins. This interaction is dependent on a highly conserved, 40 amino acid sequence that makes up most of the cytoplasmic tails of the neurexins. Our data suggest a direct interaction between the cytoplasmic domains of a plasma membrane protein (the neurexins) and a protein specific for a subcellular organelle (synaptotagmin). Such an interaction could have an important role in the docking and targeting of synaptic vesicles in the nerve terminal.

Amino Acid Sequence↗

PubMed1992

Neurexins.

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Amino Acid Sequence↗