A motif of eleven amino acids is a structural adaptation that facilitates motor capability of eutherian prestin

Abstract

SummaryCochlear outer hair cells (OHCs) alter their length in response to transmembrane voltage changes. This so-called electromotility is the result of conformational changes of membrane-bound prestin. Prestin-based OHC motility is thought to be responsible for cochlear amplification, which contributes to the exquisite frequency selectivity and sensitivity of mammalian hearing. Prestin belongs to an anion transporter family, the solute carrier protein 26A (SLC26A). Prestin is unique in this family in that it functions as a voltage-dependent motor protein manifested by two hallmarks, nonlinear capacitance and motility. Evidence suggests that prestin orthologs from zebrafish and chicken are anion exchangers or transporters with no motor function. We identified a segment of 11 amino acid residues in eutherian prestin that is extremely conserved among eutherian species but highly variable among non-mammalian orthologs and SLC26A paralogs. To determine whether this sequence represents a motif that facilitates motor function in eutherian prestin, we utilized a chimeric approach by swapping corresponding residues from the zebrafish and chicken with those of gerbil. Motility and nonlinear capacitance were measured from chimeric prestin-transfected human embryonic kidney 293 cells using a voltage-clamp technique and photodiode-based displacement measurement system. We observed a gain of motor function with both of the hallmarks in the chimeric prestin without loss of transport function. Our results show, for the first time, that the substitution of a span of 11 amino acid residues confers the electrogenic anion transporters of zebrafish and chicken prestins with motor-like function. Thus, this motif represents the structural adaptation that assists gain of motor function in eutherian prestin.

The V499G/Y501H Mutation Impairs Fast Motor Kinetics of Prestin and Has Significance for Defining Functional Independence of Individual Prestin Subunits

“…Such a possibility is supported by recent studies in which electromotile SLC26 proteins were generated by replacing portions of the non-electromotile SLC26 proteins with those of electromotile prestin (35)(36)(37). For example, Tan et al (36) and Tang et al (37) succeeded in converting non-electromotile SLC26 members into electromotile SLC26 members by swapping a very short noncharged amino acid segment. These results suggest that most if not all SLC26 proteins are potentially pre-equipped with the required molecular components to become motile, such as a voltage sensor(s) and an actuator(s).…”

Prestin at year 14: Progress and prospect

“…However, the eutherian prestin is relatively invariant as demonstrated by having 98% sequence identity among four different mammalian species: human, mouse, rat and gerbil (He et al, 2006; Okoruwa et al, 2008; Tan et al, 2012). This relative invariance is even more remarkable when compared to prestin’s closest paralog, SLC26A4 (pendrin), which has 40% sequence identity with prestin (Dallos and Fakler, 2002; Mount and Romero, 2004; Tan et al, 2012). In comparison to prestin the other SLC26A paralogs do not exhibit such a high degree of conservation among eutherian species.…”

Glutamate Transporter Homolog-based Model Predicts That Anion-π Interaction Is the Mechanism for the Voltage-dependent Response of Prestin

“…The expression of truncated protein without ICF strongly suggests that these residues are not in the TM region. In addition, the adjacent signature sulfate transport (residues 127-130) (4) and motile eutherian SLC26A helper (residues 158 -178) motifs (12) further support the importance of the region encompassing the ICF structure in prestin function. Experiments that alter these motifs by site mutagenesis and/or swapping have demonstrated the functional importance of these two motifs.…”

“…The structure of our Glt Phlike model is further divided into an outer shell (TM1-TM6) and an inner core (HP1, HP2, TM7, and TM8). The unique feature of the structure is the ICF, which functionally belongs to the inner core and is neighbored in the sequence by the signature sulfate transport (4) and motile eutherian SLC26A helper motifs (12). These two motifs contribute significantly to the integrity of the unique functional properties of prestin.…”

“…Prestin can respond to voltage change (signified by the presence of a gating current) and undergo conformational change (reflected by length change of outer hair cells). Such voltage-dependent properties lie in distinct regions within the SulTP domain (residues 70 -512) (11)(12)(13)(14). Nevertheless, the underlying mechanism and the identity of residue(s) associated with the voltage sensor are still unresolved.…”