Sizing the Bacillus anthracis PA63 Channel with Nonelectrolyte Poly(Ethylene Glycols)

Abstract

Nonelectrolyte polymers of poly(ethylene glycol) (PEG) were used to estimate the diameter of the ion channel formed by the Bacillus anthracis protective antigen 63 (PA(63)). Based on the ability of different molecular weight PEGs to partition into the pore and reduce channel conductance, the pore appears to be narrower than the one formed by Staphylococcus aureus alpha-hemolysin. Numerical integration of the PEG sample mass spectra and the channel conductance data were used to refine the estimate of the pore's PEG molecular mass cutoff (approximately 1400 g/mol). The results suggest that the limiting diameter of the PA(63) pore is<2 nm, which is consistent with an all-atom model of the PA(63) channel and previous experiments using large ions.

Applications of biological pores in nanomedicine, sensing, and nanoelectronics

“…These studies, which were performed in 1992 by Krasilnikov et al , analyzed current blockages due to translocating PEG polymers of various molecular weights to determine the volume of a lumen of the α-hemolysin pore, a cytolysin pore from non- Vibrio cholerae , and a pore formed by the β-subunits of Vibrio cholerae [223 •• ]. Since then, this concept has been used to interrogate the volume of the lumen of the mitochondrial protein Toc75 (a polypeptide transporter), [210] the anthrax porin PA 7 , [73] the colicin 1a channel, [226], and connexon pores [227]. …”

Probing single nanometer-scale pores with polymeric molecular rulers

“…In addition, Krasilnikov and others used PEGs to estimate the radii of ion channels from the ability of size-selected PEGs to partition into the channel pore. 11,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Protein translocation across membranes, which plays a key role in many biological processes, can be facilitated by ion channels. [37][38][39] Other biomolecules can be detected as they transport through ion channels.…”

Study of the Protein Complex, Pore Diameter, and Pore-forming Activity of the Borrelia burgdorferi P13 Porin

“…From the experiments with NEs we calculated a diameter of about 1.4 nm for the P13 complex. These calculations include an estimated error of Ϯ0.1 nm caused by a certain smearing of the molecular masses of the individual NEs influencing their hydrodynamic radii (45,56). According to our results, a constriction inside the P13 channel cannot be excluded completely, but this is rather unlikely because the constriction has a similar diameter as the channel opening as judged from the results of estimating the channel filling.…”

“…Size of the Pore Formed by the P13 Complex-We used different NEs to determine the channel diameter of the P13 pore employing a previously suggested method (43,45,56). Because NEs are uncharged molecules, they avoid attraction/repulsion forces between ions and charges in the channel interior.…”