Abstract
BackgroundATP-binding cassette (ABC) transporters are involved in the active transportation of various endogenous or exogenous substances. Two ABCG2 gene subfamily members have been identified in birds. A detailed comparative study of the ABCG2 and ABCG2-like genes aid our understanding of their evolutionary history at the molecular level and provide a theoretical reference for studying the specific functions of ABCG2 and ABCG2-like genes in birds.ResultsWe first identified 77 ABCG2/ABCG2-like gene sequences in the genomes of 41 birds. Further analysis showed that both the nucleic acid and amino acid sequences of ABCG2 and ABCG2-like genes were highly conserved and exhibited high homology in birds. However, significant differences in the N-terminal structure were found between the ABCG2 and ABCG2-like amino acid sequences. A selective pressure analysis showed that the ABCG2 and ABCG2-like genes were affected by purifying selection during the process of bird evolution.ConclusionsWe believe that multiple members of the ABCG2 gene subfamily exist on chromosome 4 in the ancestors of birds. Over the long course of evolution, only the ABCG2 gene was retained on chromosome 4 in birds. The ABCG2-like gene on chromosome 6 might have originated from chromosome replication or fusion. The structural differences between the N terminus of ABCG2 protein and those of ABCG2-like proteins might lead to functional differences between the corresponding genes.
Highlights
ATP-binding cassette (ABC) transporters are involved in the active transportation of various endogenous or exogenous substances
Combined with the current National Center for Biotechnology Information (NCBI) nomenclature system, the BLAST results suggested that only two ATP-binding cassette subfamily G member 2 (ABCG2) gene subfamily members, i.e., the ABCG2 and ABCG2-like genes, exist in birds
Phylogenetic analysis A maximum likelihood (ML) phylogenetic analysis (Fig. 1) was performed using the nucleic acid sequences of the ABCG2 and ABCG2-like genes, which were obtained from all birds (Additional file 1, Table S1) and outgroup species (Additional file 2, Table S3)
Summary
ATP-binding cassette (ABC) transporters are involved in the active transportation of various endogenous or exogenous substances. The ATP-binding cassette (ABC) subfamily G member 2 (junior blood group) (ABCG2) gene is the second member of the G subfamily of ABC transporters and is considered the breast cancer resistance protein (BCRP) gene [1, 2]. The ABCG2/BCRP protein is mainly distributed in tissues with secretory and excretory functions, Ma et al BMC Evolutionary Biology (2020) 20:85. The members of the ABC transporter superfamily in most mammals can be classified into seven subfamilies (from A to G) [14], and each of these subfamilies might have undergone a long evolutionary process, from single structures to half structures or ABC2 structures, and from half structures to full structures (simple to complex structures). Some ABC proteins have lost their TMD, which leads to changes in their basic functions (e.g., ABCE and ABCF). During the evolution of the seven full-structure ABC transporters, ABCA, ABCB, ABCC and ABCG originated before the last eukaryotic common ancestor (LECA), whereas the ABCD, ABCE and ABCF families originated before terrestrial plants, archaea, and the differentiation between bacteria and archaea, respectively
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