Hypothesis: A helix of ankyrin repeats of the NOMPC-TRP ion channel is the gating spring of mechanoreceptors

Abstract

rich rock increases local field strength enough to alter map readings but not compass direction, should leave the birds reoriented or disoriented. Indeed, at smooth gradients they are reoriented, whereas at irregular ones they are ludicrously disoriented (Figure 3).Pigeons, like most animals with maps, possess enormous numbers of magnetite grains in the ethymoid sinus. There are species in which magnetic sensitivity may be mediated in other ways, for example magnetic induction in elasmobranchs, or paramagnetic effects in the visual pigments of silvereye birds, but magnetitebased compasses seem to fit the behavioral data in nearly all cases. In species using a map for navigation, there are far too many of these grains for a mere compass, but enough to easily determine map location at least at an order of magnitude better than the 2 km estimated from returns of visually impaired pigeons.Pigeons subjected to gradually increasing and decreasing intense magnetic fields should have their magnetite grains remagnetized. If the map sense is directional, like a typical hand compass, the birds should be disoriented. On the other hand, if the map is axial, that is, if it cannot distinguish between north and south, the orientation should be better. Birds treated with magnetic fields are indeed better oriented. However, if the birds are subjected to a sharp intense pulse, either kind of map organ should be severely impaired, which is exactly what is observed.Whichever cues the map sense involves, it seems likely that it is this information which allows low-resolution first-time migrants to achieve high-resolution returns-and high-resolution southward trips in future years. Far and away the biggest question in long-distance navigation is the nature of the map sense. Second is the issue of recalibration, which is still puzzling. The interaction of these specific learning programs doubtlessly holds many magnificent secrets. Further reading Able, K.P., and Able, M.A. (1995). Interactions in the flexible orientation system of a migratory bird. Nature 375, 230-232. Gould, J.L. (1980). The case for magnetic-field sensitivity in birds and bees.

Repeat-protein folding: New insights into origins of cooperativity, stability, and topology

“…The elongated structures of these molecules suggest a linear reaction coordinate that naturally aligns with the unidirectional retraction coordinate used in force spectroscopy. In some cases, the application of force along the long axis of linear repeat proteins may be biologically relevant, as some linear repeat-containing proteins have been proposed to act as mechanical springs within the cell [97][98][99][100][101].…”

“…The elongated structures of these molecules suggest a linear reaction coordinate that naturally aligns with the unidirectional retraction coordinate used in force spectroscopy. In some cases, the application of force along the long axis of linear repeat proteins may be biologically relevant, as some linear repeat-containing proteins have been proposed to act as mechanical springs within the cell [97][98][99][100][101].Forced unfolding studies of Ankyrin-B, a 24 repeat cytoskeletal protein have revealed two different forced unfolding events [97]. At low extensions, a linear force-displacement relationship is seen up to forces of 100pN, which the authors interpret as Hookean distortion of a fairly rigid superhelical ankyrin stack.…”

Nanospring behaviour of ankyrin repeats

“…Visual inspection of the extrapolated structure of 24 ankyrin-R repeats 2 indicates the possibility of spring-like behaviour of the putative superhelix. Moreover, stacks of 17-29 ankyrin repeats in the cytoplasmic domains of transient receptor potential (TRP) channels have been identified as candidates for a spring that gates mechanoreceptors in hair cells as well as in Drosophila bristles [3][4][5] . Here we report that tandem ankyrin repeats exhibit tertiary-structure-based elasticity and behave as a linear and fully reversible spring in single-molecule measurements by atomic force microscopy.…”

Structure-function analysis of TRPV channels

“…For the chloroplast protein SRP43 it has been shown that its third and fourth ANK repeats are involved in dimerization of the protein (Jonas-Straube et al 2001) and two recent studies demonstrate the importance of ANK repeats for the tetramerization of TRPV6 and TRPV5 ion channels Erler et al 2004). A very interesting hypothesis for the functional role for the 29 ANK repeat containing Drosophila NOMPC channel is that this repeat structure forms the gating spring of mechanoreceptors (Howard and Bechstedt 2004). Vertebrate TRPA1 channels that are candidates for the mechanosensitive transduction channel of hair cells only contain 17 ANK repeats, which may still confer sufficient gating spring stiffness (Corey et al 2004).…”