Protein electrostriction: a possibility of elastic deformation of the alpha-hemolysin channel by the applied field.
While conformational flexibility of proteins is widely recognized as one of their functionally crucial features and enjoys proper attention for this reason, their elastic properties are rarely discussed. In ion channel studies, where the voltage-induced or ligand-induced conformational transitions, gating, are the leading topic of research, the elastic structural deformation by the applied electric field has never been addressed at all. Here we examine elasticity using a model channel of known crystal structure-Staphylococcus aureus alpha-hemolysin. Working with single channels reconstituted into planar lipid bilayers, we first show that their ionic conductance is asymmetric with voltage even at the highest salt concentration used where the static charges in the channel interior are maximally shielded. Second, choosing 18-crown-6 as a molecular probe whose size is close to the size of the narrowest part of the alpha-hemolysin pore, we analyze the blockage of the channel by the crown/K(+) complex. Analysis of the blockage within the framework of the Woodhull model in its generalized form demonstrates that the model is able to correctly describe the crown effect only if the parameters of the model are considered to be voltage-dependent. Specifically, one has to include either a voltage-dependent barrier for crown release to the cis side of the channel or voltage-dependent interactions between the binding site and the crown. We suggest that the voltage sensitivity of both the ionic conductance of the channel seen at the highest salt concentration and its blockage by the crown reflects a field-induced deformation of the pore.
Krasilnikov
Oleg V
OV
Laboratory of Membrane Biophysics, Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, Pernambuco 50670-901, Brazil. kras@ufpe.br
Merzlyak
Petr G
PG
Yuldasheva
Liliya N
LN
Capistrano
Maria F
MF
D001427:Bacterial Toxins / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D047248:Crown Compounds / Q000737:chemistry; D004307:Dose-Response Relationship, Radiation; D004548:Elasticity; D004574:Electromagnetic Fields; D006460:Hemolysin Proteins; D015640:Ion Channel Gating / Q000528:radiation effects*; D008051:Lipid Bilayers / Q000737:chemistry* / Q000528:radiation effects*; D008560:Membrane Fluidity / Q000528:radiation effects; D008956:Models, Chemical; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000528:radiation effects; D016062:Porosity / Q000528:radiation effects; D011487:Protein Conformation / Q000528:radiation effects; D011829:Radiation Dosage
D001427:Bacterial Toxins; D047248:Crown Compounds; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C021091:staphylococcal alpha-toxin; C021016:1,2-diphytanoylphosphatidylcholine