The human ABCG2 multidrug transporter plays a crucial role in the absorption and excretion
of xeno- and endobiotics, contributes to cancer drug resistance and the development
of gout. In this work, we have analyzed the effects of selected variants, residing
in a structurally unresolved cytoplasmic region (a.a. 354–367) of ABCG2 on the function
and trafficking of this protein. A cluster of four lysines (K357–360) and the phosphorylation
of a threonine (T362) residue in this region have been previously suggested to significantly
affect the cellular fate of ABCG2. Here, we report that the naturally occurring K360del
variant in human cells increased ABCG2 plasma membrane expression and accelerated
cellular trafficking. The variable alanine replacements of the neighboring lysines
had no significant effect on transport function, and the apical localization of ABCG2
in polarized cells has not been altered by any of these mutations. Moreover, in contrast
to previous reports, we found that the phosphorylation-incompetent T362A, or the phosphorylation-mimicking
T362E variants in this loop had no measurable effects on the function or expression
of ABCG2. Molecular dynamics simulations indicated an increased mobility of the mutant
variants with no major effects on the core structure of the protein. These results
may help to decipher the potential role of this unstructured region within this transporter.
