Abstract
Purpose:
In dark-adapted rods the bulk of arrestin-1 is localized away from the outer segment, where its key binding partner rhodopsin resides. Two factors were proposed to contribute to this counter-intuitive localization of arrestin-1: its binding to microtubules, concentrated in the inner segment, perinucler area, and synaptic terminals, or relatively large size of arrestin-1 dimers and tetramers, which it readily forms at physiological expression level.
Methods:
We created transgenic mice expressing constitutively monomeric arrestin-1 mutant at different levels, from 10 to ~300% of normal WT arrestin-1 concentration in rods. Since the mutant binds both rhodopsin and microtubules normally, this eliminated a single factor that can contribute to arrestin-1 distribution, its self-association. Arrestin distribution in fixed eyes from dark-adapted WT and transgenic mice expressing this mutant was compared by immunohistochemistry.
Results:
The distribution of constitutively monomeric arrestin-1 in dark-adapted rods was remarkably similar to the distribution of WT arrestin-1, which robustly self-associates, so that the majority of arestin-1 complement exists as a tetramer in WT rods in the dark. Self-association-deficient arrestin-1 was largely localized to the inner segments, cell bodies, and synaptic terminals, just like WT protein, with relatively small fraction present in the outer segments.
Conclusions:
These data suggest that the size of arestin-1 dimers and tetramers, which are expected to be too large to fit into intra-discal spaces in the outer segments, is not the dominant factor keeping arrestin-1 away from this compartment in the dark. Thus, arrestin-1 distribution in dark-adapted photoreceptors is largely determined by its interactions with to microtubules and/or other binding partners absent in the outer segments. Supported by NIH grant EY011500.
Keywords: 648 photoreceptors •
659 protein structure/function •
714 signal transduction