Abstract
Within major facilitator superfamily (MFS), up to 27 unknown major facilitator families and many members of 60 well-characterized families have been functionally unknown as yet, due to their sharing no or significantly low sequence identity with characterized MFS members. Here we present the first report on the characterization of one functionally unknown MFS transporter designated MdrP with the accession version No. ANU18183.1 from the slight halophile Planococcus maritimus DS 17275T. During the screening of Na+/H+ antiporter genes, we found at first that MdrP exhibits Na+(Li+, K+)/H+ antiport activity, and propose that it should represent a novel class of Na+(Li+, K+)/H+ antiporters. However, we speculate that MdrP may possess an additional protein function. The existence of the signature Motif A of drug/H+antiporter (DHA) family members and phylogenetic analysis suggest that MdrP may also function as a drug efflux pump, which was established by minimum inhibitory concentration tests and drug efflux activity assays. Taken together, this novel MFS transporter exhibits dual functions as a Na+(Li+, K+)/H+ antiporter and a multidrug efflux pump, which will be very helpful to not only positively contribute to the function prediction of uncharacterized MFS members especially DHA1 family ones, but also broaden the knowledge of Na+/H+ antiporters.
Highlights
IntroductionMajor facilitator superfamily (MFS) is the largest and most diverse known superfamily of secondary transporters widely distributed throughout the whole living world (Pao et al, 1998; Law et al, 2008; Reddy et al, 2012), which has been currently divided into 87 recognized families with more than one million sequenced members on the basis of phylogenetic analysis in the TransporterCharacterization of a Functionally Unknown major facilitator superfamily (MFS) TransporterClassification Database (TCDB) (Saier et al, 2016)
ORF1 beginning from No 1 bp encodes a N-terminus truncated protein with no initiation codon, which corresponds with 100% identity to the partial amino acid sequence from No 146 residue to No 709 residue of one putative DNA helicase designated UvrD from P. maritimus DSM 17275T (Supplementary Figure S1)
ORF2 encodes an intact protein with an initiation codon and a stop codon, which corresponds with 100% identity to one uncharacterized major facilitator superfamily (MFS) transporter from P. maritimus DSM 17275T (Supplementary Figure S1)
Summary
Major facilitator superfamily (MFS) is the largest and most diverse known superfamily of secondary transporters widely distributed throughout the whole living world (Pao et al, 1998; Law et al, 2008; Reddy et al, 2012), which has been currently divided into 87 recognized families with more than one million sequenced members on the basis of phylogenetic analysis in the TransporterCharacterization of a Functionally Unknown MFS TransporterClassification Database (TCDB) (Saier et al, 2016). Major facilitator superfamily (MFS) is the largest and most diverse known superfamily of secondary transporters widely distributed throughout the whole living world (Pao et al, 1998; Law et al, 2008; Reddy et al, 2012), which has been currently divided into 87 recognized families with more than one million sequenced members on the basis of phylogenetic analysis in the Transporter. Characterization of a Functionally Unknown MFS Transporter. For topological and sequential characteristics, most MFS transporters consist of either 12, 14, or occasionally, 24 transmembrane segments (TMSs) containing 400 to 600 amino acid residues (Pao et al, 1998; Law et al, 2008; Reddy et al, 2012). Each well-characterized family within MFS includes many members derived from the genome sequencing projects, whose functions have been unascertained as yet due to their significantly low sequence identity with the characterized members (Saier et al, 2016)
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