As always, I am pressed for time, so let me introduce you to the protein which appears to have helped guide the independent appearance of echolocation – prestin – with a few cut-and-pastes.
Since prestin is a membrane protein found in mammalian cells that act as hearing receptors, here is a figure that shows the anatomical context of these cells:
Now, consider the descriptions from the following abstracts/web pages:
Nature. 2000 May 11;405(6783):149-55.
Prestin is the motor protein of cochlear outer hair cells.
Zheng J, Shen W, He DZ, Long KB, Madison LD, Dallos P
The outer and inner hair cells of the mammalian cochlea perform different functions. In response to changes in membrane potential, the cylindrical outer hair cell rapidly alters its length and stiffness. These mechanical changes, driven by putative molecular motors, are assumed to produce amplification of vibrations in the cochlea that are transduced by inner hair cells. Here we have identified an abundant complementary DNA from a gene, designated Prestin, which is specifically expressed in outer hair cells. Regions of the encoded protein show moderate sequence similarity to pendrin and related sulphate/anion transport proteins. Voltage-induced shape changes can be elicited in cultured human kidney cells that express prestin. The mechanical response of outer hair cells to voltage change is accompanied by a ‘gating current’, which is manifested as nonlinear capacitance. We also demonstrate this nonlinear capacitance in transfected kidney cells. We conclude that prestin is the motor protein of the cochlear outer hair cell.
Nat Rev Mol Cell Biol. 2002 Feb;3(2):104-11.
Prestin, a new type of motor protein.
Dallos P, Fakler B
Prestin, a transmembrane protein found in the outer hair cells of the cochlea, represents a new type of molecular motor, which is likely to be of great interest to molecular cell biologists. In contrast to enzymatic-activity-based motors, prestin is a direct voltage-to-force converter, which uses cytoplasmic anions as extrinsic voltage sensors and can operate at microsecond rates. As prestin mediates changes in outer hair cell length in response to membrane potential variations, it might be responsible for sound amplification in the mammalian hearing organ.
And then there is this:
Prestin is the motor protein of the outer hair cells. It is highly expressed in the outer hair cells, and is not expressed in the nonmotile inner hair cells. It was identified using a cDNA library subtraction procedure [Zheng et al., 2000].Immunolocalization showed prestin to be expressed in the lateral plasma membrane of the OHCs, the region where electromotility occurs. The expression pattern correlates with the appearance of OHC electromotility [Belyantseva et al., 2000]. Prestin (mol. wt. 80 kDa) is a member of a distinct family of anion transporters, SLC26. Members of this family are structurally well conserved and can mediate the electroneutral exchange of chloride and carbonate across the plasma membrane of mammalian cells [Lohi et al., 2000; Waldegger et al, 2001], two anions found to be essential for outer hair cell motility. Unlike the classical, enzymatically driven motors, the function of this new type of motor is based on direct voltage-to-displacement conversion. It acts several orders of magnitude faster than cellular motor proteins [Dallos and Fakler, 2002]. A targeted gene disruption strategy of pres showed a >100 fold loss of auditory sensitivity [Liberman et al., 2002].
Another amazing protein, eh? Next, we’ll consider this protein more extensively in the context of front-loading.