studies have suggested that SLC45A2
may be a sucrose or proton transporter
because it shares structural similarity
and the signature RXGRR motif with
sucrose/proton symporters in plants
[18, 19]. This is supported by the recent
discovery of the Drosophila melanogaster
sucrose/proton cotransporter
SCRT, which phylogenetically clusters
with the SLC45 protein family and exhibits
the highest degree of amino
acid similarity with SLC45A2 [23].
Tyrosinase processing and trafficking
is regulated by organellar pH [24], and
in addition, the crenate melanosome
found in the uw mouse mutant [22, 25]
implies disruption of osmotic balancing
that is probably due to the disruption of
sucrose transportation [22]. Taking the
evidence together, it is plausible that
SLC45A2 is a sucrose/proton symporter
and mediates melanin synthesis
by regulating organellar pH and/or
osmotic balancing.