Learn More
One cannot always distinguish different Markov models of ion-channel kinetics solely on the basis of steady-state kinetic data. If two generator (or transition) matrices are related by a similarity transformation that does not combine states with different conductances, then the models described by these generator matrices have the same observable(More)
Colicin Ia, a bacterial protein toxin of 626 amino acid residues, forms voltage-dependent channels in planar lipid bilayer membranes. We have exploited the high affinity binding of streptavidin to biotin to map the topology of the channel-forming domain (roughly 175 residues of the COOH-terminal end) with respect to the membrane. That is, we have(More)
The differentiation of figure from ground plays an important role in the perceptual organization of visual stimuli. The rapidity with which we can discriminate the inside from the outside of a figure suggests that at least this step in the process may be performed in visual cortex by a large number of neurons in several different areas working together in(More)
Fixed negative charges in many cation channels raise the single-channel conductance, apparently by an electrostatic mechanism: their effects are accentuated in solutions of low ionic strength and attenuated at high ionic strength. The charges of specific amino acids near the ends of the proposed pore-lining M2 segment of the nicotinic acetylcholine(More)
Learning to recognize mirror, rotational and translational symmetries is a difficult problem for massively-parallel network models. These symmetries cannot be learned by first-order perceptrons or Hopfield networks, which have no means for incorporating additional adaptive units that are hidden from the input and output layers. We demonstrate that the(More)
Charge selectivity in ion channel proteins is not fully understood. We have studied charge selectivity in a simple model system without charged groups, in which an amphiphilic helical peptide, Ac-(Leu-Ser-Ser-Leu-Leu-Ser-Leu)3-CONH2, forms ion channels across an uncharged phospholipid membrane. We find these channels to conduct both K+ and Cl-, with a(More)
Low pH triggers the translocation domain of diphtheria toxin (T-domain), which contains 10 α helices, to insert into a planar lipid bilayer membrane, form a transmembrane channel, and translocate the attached catalytic domain across the membrane. Three T-domain helices, corresponding to TH5, TH8, and TH9 in the aqueous crystal structure, form transmembrane(More)
Colicin Ia, a 626-residue bactericidal protein, consists of three domains, with the carboxy-terminal domain (C domain) responsible for channel formation. Whole colicin Ia or C domain added to a planar lipid bilayer membrane forms voltage-gated channels. We have shown previously that the channel formed by whole colicin Ia has four membrane-spanning segments(More)
The bacterial toxin colicin Ia forms voltage-gated channels in planar lipid bilayers. The toxin consists of three domains, with the carboxy-terminal domain (C-domain) responsible for channel formation. The C-domain contributes four membrane-spanning segments and a 68-residue translocated segment to the open channel, whereas the upstream domains and the(More)