Barium Activates Rat Cerebellar Nitric Oxide Synthase

Hsieh

Proc. Natl. Acad. Sci. U.S.A.

et al. 2009

124

In this study, we describe a highly sensitive and reusable silicon nanowire field-effect transistor for the detection of protein-protein interactions. This reusable device was made possible by the reversible association of glutathione S-transferase-tagged calmodulin with a glutathione modified transistor. The calmodulin-modified transistor exhibited selective electrical responses to Ca 2þ (≥1 μM) and purified cardiac troponin I (∼7 nM); the change in conductivity displayed a linear dependence on the concentration of troponin I in a range from 10 nM to 1 μM. These results are consistent with the previously reported concentration range in which the dissociation constant for the troponin I-calmodulin complex was determined. The minimum concentration of Ca 2þ required to activate calmodulin was determined to be 1 μM. We have also successfully demonstrated that the N-type Ca 2þ channels, expressed by cultured 293T cells, can be recognized specifically by the calmodulin-modified nanowire transistor. This sensitive nanowire transistor can serve as a high-throughput biosensor and can also substitute for immunoprecipitation methods used in the identification of interacting proteins.calcium ion | glutathione S-transfrease | N-type calcium channel | silicon nanowire field-effect transistor

Section: Supporting Information)supporting

confidence: 88%

Label-free detection of protein-protein interactions using a calmodulin-modified nanowire transistor

Hsieh

Proc. Natl. Acad. Sci. U.S.A.

et al. 2009

124

Progress in Biophysics and Molecular Biology

“…However, I Ba inactivation depends on Ba flux, and it seems clear now that Ba can recapitulate a weak version of CDI. Ba is known to complex with CaM and activate interaction with CaM targets (Ozawa et al, 1999; Yamazaki et al, 1996), but its apparent affinity in other systems has typically been ≥100-fold lower than for Ca. While our change in rate constants that produces appropriate I Ba CDI could be construed to represent only a ~10-fold reduction in affinity, this lower value should not be taken to imply an actual affinity difference in the classical biochemical sense.…”

Section: Discussionmentioning

confidence: 99%

Interplay of voltage and Ca-dependent inactivation of L-type Ca current

Grandi

Morotti

Ginsburg

et al. 2010

Inactivation of L-type Ca channels (LTCC) is regulated by both Ca and voltage-dependent processes (CDI and VDI). To differentiate VDI and CDI, several experimental and theoretical studies have considered the inactivation of Ba current through LTCC (IBa) as a measure of VDI. However, there is evidence that Ba can weakly mimic Ca, such that IBa inactivation is still a mixture of CDI and VDI. To avoid this complication, some have used the monovalent cation current through LTCC (INS), which can be measured when divalent cation concentrations are very low. Notably, INS inactivation rate does not depend on current amplitude, and hence may reflect purely VDI. However, based on analysis of existent and new data, and modeling, we find that INS can inactivate more rapidly and completely than IBa, especially at physiological temperature. Thus VDI that occurs during IBa (or ICa) must differ intrinsically from VDI during INS. To account for this, we have extended a previously published LTCC mathematical model of VDI and CDI into an excitation-contraction coupling model, and assessed whether and how experimental IBa inactivation results (traditionally used in VDI experiments and models) could be recapitulated by modifying CDI to account for Ba-dependent inactivation. Thus, the view of a slow and incomplete INS inactivation should be revised, and INS inactivation is a poor measure of VDI during ICa or IBa. This complicates VDI analysis experimentally, but raises intriguing new questions about how the molecular mechanisms of VDI differ for divalent and monovalent currents through LTCCs.

Acta Crystallogr F Struct Biol Cryst Commun

“…While Pb has been shown to activate CaM effectively and in fact has a higher affinity than Ca (Fullmer et al, 1985;Richardt et al, 1986;Ouyang & Vogel, 1998), Ba activation requires an around 200-fold higher concentration than Ca for CaM activation (Kreye et al, 1986;Yamazaki et al, 1996). These observations can be explained at least in part by the variations in the ionic radii of these ions and by the differences in metal-ion coordination distances in the EF-hands in the complexes: these would be expected to be reflected in the actual affinity.…”

Section: Discussionmentioning

confidence: 99%

“…Ba 2+ and Mg 2+ have been reported to have significantly lower, if any, affinity towards CaM (Ozawa et al, 1999). For example, the CaM-regulated activation of cerebellar nitric oxide synthase requires an over 200-fold higher concentration of Ba 2+ than of Ca 2+ (Yamazaki et al, 1996) and the interaction between CaM and caldesmon is weakened by the exchange of Ca 2+ for Ba 2+ (Huber et al, 1996). On the other hand, Mg 2+ levels in the cellular environment are much higher than those of Ca 2+ and CaM must be able to function specifically in the presence of an excess of Mg 2+ ions (Malmendal et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

A structural insight into lead neurotoxicity and calmodulin activation by heavy metals

Kursula

Majava

2007

Calmodulin is a calcium sensor that is also capable of binding and being activated by other metal ions. Of specific interest in this respect is lead, which is known to be neurotoxic and to have a very high affinity towards calmodulin. Crystal structures of human calmodulin complexed with lead and barium ions have been solved. The results will help in understanding the activation mechanisms of calmodulin by different heavy metals and will provide a detailed view of a putative target for lead neurotoxicity in humans.