scholarly journals Determinants of cation transport selectivity: Equilibrium binding and transport kinetics

2015 ◽  
Vol 146 (1) ◽  
pp. 3-13 ◽  
Author(s):  
Steve W. Lockless
Keyword(s):  
Binding Sites ◽  
Protein Structures ◽  
Cation Transport ◽  
Transport Processes ◽  
Ion Binding ◽  
Nonselective Cation Channels ◽  
Equilibrium Binding ◽  
Ion Binding Sites ◽  
Primary Focus ◽  
The Relationship

The crystal structures of channels and transporters reveal the chemical nature of ion-binding sites and, thereby, constrain mechanistic models for their transport processes. However, these structures, in and of themselves, do not reveal equilibrium selectivity or transport preferences, which can be discerned only from various functional assays. In this Review, I explore the relationship between cation transport protein structures, equilibrium binding measurements, and ion transport selectivity. The primary focus is on K+-selective channels and nonselective cation channels because they have been extensively studied both functionally and structurally, but the principles discussed are relevant to other transport proteins and molecules.

scholarly journals Accessibility of Cations to the Selectivity Filter of KcsA in the Inactivated State: An Equilibrium Binding Study

2019 ◽  
Vol 20 (3) ◽  
pp. 689 ◽  
Author(s):  
Ana Giudici ◽  
Maria Renart ◽  
Clara Díaz-García ◽  
Andrés Morales ◽  
José Poveda ◽  
...  
Keyword(s):  
Potassium Channel ◽  
Binding Sites ◽  
Cation Binding ◽  
Selectivity Filter ◽  
Ion Binding ◽  
Channel State ◽  
Equilibrium Conditions ◽  
Equilibrium Binding ◽  
Potassium Channel Kcsa ◽  
Ion Binding Sites

Cation binding under equilibrium conditions has been used as a tool to explore the accessibility of permeant and nonpermeant cations to the selectivity filter in three different inactivated models of the potassium channel KcsA. The results show that the stack of ion binding sites (S1 to S4) in the inactivated filter models remain accessible to cations as they are in the resting channel state. The inactivated state of the selectivity filter is therefore “resting-like” under such equilibrium conditions. Nonetheless, quantitative differences in the apparent KD’s of the binding processes reveal that the affinity for the binding of permeant cations to the inactivated channel models, mainly K+, decreases considerably with respect to the resting channel. This is likely to cause a loss of K+ from the inactivated filter and consequently, to promote nonconductive conformations. The most affected site by the affinity loss seems to be S4, which is interesting because S4 is the first site to accommodate K+ coming from the channel vestibule when K+ exits the cell. Moreover, binding of the nonpermeant species, Na+, is not substantially affected by inactivation, meaning that the inactivated channels are also less selective for permeant versus nonpermeant cations under equilibrium conditions.

scholarly journals Synthesis and Photoregulated Metal Coordination of Azobenzene Polymer Having Ion Binding Sites

1991 ◽  
Vol 23 (2) ◽  
pp. 127-134 ◽  
Author(s):  
Masato Nanasawa ◽  
Takahiro Nishiyama ◽  
Hiroyoshi Kamogawa
Keyword(s):  
Binding Sites ◽  
Metal Coordination ◽  
Ion Binding ◽  
Azobenzene Polymer ◽  
Ion Binding Sites

The Effect Of Metal Ions On Human Factor IX Antigenicity

1981 ◽  
Author(s):  
R M Lewis ◽  
H M Reisner ◽  
B C Abels ◽  
H R Roberts
Keyword(s):  
Divalent Cation ◽  
Binding Sites ◽  
Human Factor ◽  
Antibody Binding ◽  
Factor Ix ◽  
Ion Binding ◽  
Human Factor Ix ◽  
Excess Mg ◽  
Ion Binding Sites ◽  
Two Populations

Affinity chromatography of an inhibitor to human factor IX (F.IX) separated the antibody into two populations. The ion dependent population of antibodies had an absolute divalent cation (Me++) binding requirement. The non-ion dependent population bound F.IX equally in the presence or absence of Me++. The concentration of Me++ required for ½ the maximum ion dependent antibody binding (½ max) was (in nM) Ca++ 0.40, Mn++ 0.05, Sr++ 0.70 and Mg++ 0.65.Ca++ potentiated the binding of antibody in the presence of excess Mg++. In addition, the ½ max for Ca++ was reduced about four fold. These observations are consistent with separate binding sites on the F.IX molecule for Ca++ and Mg++ and potentiation of Ca++ binding by Mg++. Scat- chard analysis of ion dependent antibody binding indicates about a 10 fold greater affinity of antibody in the presence of Ca++ than Mg++. In the presence of both cations, affinity was at least as high as in the presence of Ca++ alone supporting the presence of separate ion binding sites on the F.IX molecule.

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