Low-voltage-activated Ca sub(V)3 channels are distinguished among other voltage-activated calcium channels by the most negative voltage activation threshold. The voltage dependence of current ...activation is virtually identical in all three Ca sub(V)3 channels while the current kinetics of the Ca sub(V)3.3 current is one order slower than that of the Ca sub(V)3.1 and Ca sub(V)3.2 channels. We have analyzed the voltage dependence and kinetics of charge (Q) movement in human recombinant Ca sub(V)3.3 and Ca sub(V)3.1 channels. The voltage dependence of voltage sensor activation (Q sub(on)-V) of the Ca sub(V)3.3 channel was significantly shifted with respect to that of the Ca sub(V)3.1 channel by +18.6 mV and the kinetic of Q sub(on) activation in the Ca sub(V)3.3 channel was significantly slower than that of the Ca sub(V)3.1 channel. Removal of the gating brake in the intracellular loop connecting repeats I and II in the Ca sub(V)3.3 channel in the ID12 mutant channel shifted the Q sub(on)-V relation to a value even more negative than that for the Ca sub(V)3.1 channel. The kinetic of Q sub(on) activation was not significantly different between ID12 and Ca sub(V)3.1 channels. Deletion of the gating brake in the Ca sub(V)3.1 channel resulted in a GD12 channel with the voltage dependence of the gating current activation significantly shifted toward more negative potentials. The Q sub(on) kinetic was not significantly altered. ID12 and GD12 mutants did not differ significantly in voltage dependence nor in the kinetic of voltage sensor activation. In conclusion, the putative gating brake in the intracellular loop connecting repeats I and II controls the gating current of the Ca sub(V)3 channels. We suggest that activation of the voltage sensor in domain I is limiting both the voltage dependence and the kinetics of Ca sub(V)3 channel activation.
Low-voltage-activated Ca^sub V^3 channels are distinguished among other voltage-activated calcium channels by the most negative voltage activation threshold. The voltage dependence of current ...activation is virtually identical in all three Ca^sub V^3 channels while the current kinetics of the Ca^sub V^3.3 current is one order slower than that of the Ca^sub V^3.1 and Ca^sub V^3.2 channels. We have analyzed the voltage dependence and kinetics of charge (Q) movement in human recombinant Ca^sub V^3.3 and Ca^sub V^3.1 channels. The voltage dependence of voltage sensor activation (Q^sub on^-V) of the Ca^sub V^3.3 channel was significantly shifted with respect to that of the Ca^sub V^3.1 channel by +18.6 mV and the kinetic of Q^sub on^ activation in the Ca^sub V^3.3 channel was significantly slower than that of the Ca^sub V^3.1 channel. Removal of the gating brake in the intracellular loop connecting repeats I and II in the Ca^sub V^3.3 channel in the ID12 mutant channel shifted the Q^sub on^-V relation to a value even more negative than that for the Ca^sub V^3.1 channel. The kinetic of Q^sub on^ activation was not significantly different between ID12 and Ca^sub V^3.1 channels. Deletion of the gating brake in the Ca^sub V^3.1 channel resulted in a GD12 channel with the voltage dependence of the gating current activation significantly shifted toward more negative potentials. The Q^sub on^ kinetic was not significantly altered. ID12 and GD12 mutants did not differ significantly in voltage dependence nor in the kinetic of voltage sensor activation. In conclusion, the putative gating brake in the intracellular loop connecting repeats I and II controls the gating current of the Ca^sub V^3 channels. We suggest that activation of the voltage sensor in domain I is limiting both the voltage dependence and the kinetics of Ca^sub V^3 channel activation.
Lipids not only form the backbone of biological membranes, but also serve as the source of numerous regulatory and signaling molecules. Understanding the role of lipids in the physiology of ...eukaryotic cell will help to identify mechanisms behind lipid-related human diseases. This minireview concentrates on two examples of human diseases associated with phospholipid remodeling and transport. The first is Barth syndrome, a severe rare genetic disorder. Barth syndrome is the first recognized human disease in which the primary causative factor is a defective remodeling of the signature mitochondrial phospholipid cardiolipin. The other example involves defects associated with lipid transfer proteins (LTPs). LTPs regulate diverse lipid-mediated cellular processes important for maintaining the specific composition of different cellular organelles. In vitro LTPs facilitate lipid transport between membranes through an aqueous environment. This article is not intended to be a comprehensive review of lipid-related human diseases; its aim is rather to stress the importance of basic lipid research in our advancement in the diagnosis and treatment of diseases.
Sec14p of the yeast Saccharomyces cerevisiae is involved in protein secretion and regulation of lipid synthesis and turnover in vivo, but acts as a phosphatidylinositol–phosphatidylcholine transfer ...protein in vitro. In this work, the five homologues of Sec14p, Sfh1p–Sfh5p, were subjected to biochemical and cell biological analysis to get a better view of their physiological role. We show that overexpression of SFH2 and SFH4 suppressed the sec14 growth defect in a more and SFH1 in a less efficient way, whereas overexpression of SFH3 and SFH5 did not complement sec14. Using C‐terminal yEGFP fusions, Sfh2p, Sfh4p and Sfh5p are mainly localized to the cytosol and microsomes similar to Sec14p. Sfh1p was detected in the nucleus and Sfh3p in lipid particles and in microsomes. In contrast to Sec14p, which inhibits phospholipase D1 (Pld1p), overproduction of Sfh2p and Sfh4p resulted in the activation of Pld1p‐mediated phosphatidylcholine turnover. Interestingly, Sec14p and the two homologues Sfh2p and Sfh4p downregulate phospholipase B1 (Plb1p)‐mediated turnover of phosphatidylcholine in vivo. In summary, Sfh2p and Sfh4p are the Sec14p homologues with the most pronounced functional similarity to Sec14p, whereas the other Sfh proteins appear to be functionally less related to Sec14p.
The plasma membrane is the first line of cell defense against changes in external environment, thus its integrity and functionality are of utmost importance. The plasma membrane properties depend on ...both its protein and lipid composition. The PDR16 gene is involved in the control of Kluyveromyceslactis susceptibility to drugs and alkali metal cations. It encodes the homologue of the major K. lactis phosphatidylinositol transfer protein Sec14p. Sec14p participates in protein secretion, regulation of lipid synthesis, and turnover in vivo. We report here that the plasma membrane of the Klpdr16Δ mutant is hyperpolarized and its fluidity is lower than that of the parental strain. In addition, protoplasts prepared from the Klpdr16Δ cells display decreased stability when subjected to hypo-osmotic conditions. These changes in membrane properties lead to an accumulation of radiolabeled fluconazole and lithium cations inside mutant cells. Our results point to the fact that the PDR16 gene of K. lactis (KlPDR16) influences the plasma membrane properties in K. lactis that lead to subsequent changes in susceptibility to a broad range of xenobiotics.
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