In the preceding, accompanying article, we present models of the structure and voltage-dependent gating mechanism of the KvAP bacterial K+ channel that are based on three types of evidence: crystal structures of portions of the KvAP protein, theoretical modeling criteria for membrane proteins, and biophysical studies of the properties of native and mutated voltage-gated channels. Most of the la...

Control systems for shakers are necessary to remove both shaker dynamics as well as coupling effects between the shaker and the structure under test. Little attention has been given to shaker control for nonlinear structures. This paper presents the design, implementation and results of a shaker controller for a horizontal, cantilevered beam subjected to a non-uniform magnetic field. The object...

Voltage-gated potassium (Kv) channel gating involves complex structural rearrangements that regulate the ability of channels to conduct K(+) ions. Fluorescence-based approaches provide a powerful technique to directly report structural dynamics underlying these gating processes in Shaker Kv channels. Here, we apply voltage clamp fluorimetry, for the first time, to study voltage sensor motions i...

Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous c...

Lowering external pH reduces peak current and enhances current decay in Kv and Shaker-IR channels. Using voltage-clamp fluorimetry we directly determined the fate of Shaker-IR channels at low pH by measuring fluorescence emission from tetramethylrhodamine-5-maleimide attached to substituted cysteine residues in the voltage sensor domain (M356C to R362C) or S5-P linker (S424C). One aspect of the...

Voltage-gated potassium channels are formed by the tetramerization of their alpha subunits, in a process that is controlled by their conserved N-terminal T1 domains. The crystal structures of Shaker and Shaw T1 domains reveal interesting differences in structures that are contained within a highly conserved BTB/POZ domain fold. The most surprising difference is that the Shaw T1 domain contains ...

The Shaker locus of Drosophila melanogaster encodes a family of A-type potassium channel subunits. Shaker mutants behave as antimorphs in gene dosage tests. This behaviour is due to the production of truncated A-channel subunits. We propose that they interfere with the function of their normal counterpart by forming multimeric A-channel structures. This hypothesis was tested by constructing tra...

Single, double, and triple mutations progressively shift Shaker activation to more hyperpolarized potentials, resulting in an increase in the fraction of inactivated channels at negative resting voltages. The most negatively shifted mutation, the triple mutant, behaves like an inward rectifier. What is usually considered activation of an inward rectifier is, for the triple mutant, recovery from...

Heteromultimeric interactions of K+ channel subunits across different families have been thought to contribute to the functional diversity of ionic currents, as suggested by previous genetic evidence. We present here direct demonstration in Xenopus oocytes that subunits from distinct eag and Shaker families functionally interact, most likely as heteromultimeric channels. Coexpression with eag a...

This paper presents an axisymmetric rotational inertia shaker for reducing the structure borne noise radiated by rotating machinery. This modular inertia shaker uses a piezostack to generate a compensating force on a rotating element by accelerating a ring shaped mass. The piezostack is controlled using an adaptive shunt circuit, which emulates the impedance of a variable inductance. The inerti...