ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

Abstract

ATP-binding cassette (ABC) protein superfamily comprised of eight distinct subfamilies is known to play in fundamental biological processes and is highly conserved across animal taxa. The ABC proteins function as an active transporter with a wide substrate spectrum across the cellular membrane by using ATP cleavage as an energy source. As this superfamily is derived from the common ancestor, ABC genes have been evolved via lineage-specific duplication under selection pressure of the adaptation to their ambient environment. Here I summarized information of ABC gene families in aquatic invertebrates in the view of their evolution and putative functions in defense mechanism through phylogenetic analysis on their evolutionary significance with further functional analyze. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was highlighted with the absence of ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a gene loss event of Abcg2 has occurred sporadically in Ecdysozoa and Platyzoa during divergency of Protostome to Lophotrochozoa. Furthermore, the ecotoxicological significance of MXR is discussed in the view of MXR-mediated efflux transporters in response to various aquatic environmental pollutants. Specifically, the conserved protective function of P-glycoprotein (P-gp) and multidrug-associated proteins (MRPs) in the copepod T. japonicus, P. nana, and the rotifer B. koreanus was validated and their potential protective roles in response to various environmental pollutants such as metals, pharmaceuticals, and polycyclic aromatic hydrocarbon (PAHs) were revealed. This study provides new insight into the diversity of the entire ABC subfamily in aquatic invertebrates which will be helpful for a better understanding of the comparative evolution of aquatic invertebrates with further protective roles of MXR in response to environmental pollutants.