The Functional Specialization of Exomer as a Cargo Adaptor During the Evolution of Fungi

ANTON, CARLOS; VALDEZ TAUBAS, JAVIER; RONCERO, CESAR

GENETICS

GENETICS SOC AM

Año: 2018

0016-6731

Yeast exomer is a heterotetrameric complex assembled at the trans-Golgi network (TGN) that is required for the delivery of a distinct set of proteins to the plasma membrane using ChAPs proteins Chs6 and Bch2 as dedicated cargo adaptors. Our results show, however, a significant functional divergence between them, suggesting an evolutionary specialization among the ChAPs proteins. Moreover, the characterization of exomer mutants in several fungi indicates that exomer function as a cargo adaptor is a late evolutionary acquisition associated with several gene duplications of the fungal ChAPs ancestor. Initial gene duplication led to the formation of the two ChAPs families, Chs6 and Bch1, in the Saccaromycotina group, which have remained functionally redundant based on the characterization of Kluyveromyces lactis mutants. The whole genome duplication that occurred within the Saccharomyces genus facilitated a further divergence, which allowed Chs6/Bch2 and Bch1/Bud7 pairs to become specialized in specific cellular functions. We also show that the behavior of S. cerevisiae Chs3 as an exomer cargo is associated with the presence of specific cytosolic domains in this protein, which favor its interaction with exomer and AP-1 complexes. These domains are, however, not conserved in the Chs3 proteins of other fungi, suggesting they arose late in the evolution of fungi associated with the specialization of ChAPs as cargo adaptors.