Selecting for Altered Substrate Specificity Reveals the Evolutionary Flexibility of ATP-Binding Cassette Transporters.
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ABSTRACT:
SUBMITTER: Srikant S
PROVIDER: S-EPMC7243462 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Mammalian spermatozoa lose plasma membrane cholesterol during their maturation in the epididymis and during their capacitation in the female reproductive tract. While acceptors such as high-density lipoproteins (HDL) and apolipoproteins A-I (apoA-I) and J have been found in male and female reproductive tracts, transporters that mediate cholesterol efflux from plasma membranes of spermatozoa to such acceptors have not yet been defined. Candidate transporters are members of the ATP-binding cassette (ABC) transporter superfamily including ABCA1, ABCA7, ABCG1 and ABCG4, which have all been implicated in the transport of sterols and phospholipids to apolipoproteins and HDL. Here we show that mouse spermatozoa in the seminiferous tubules and epididymis express ABCA1, ABCA7 and ABCG1, but not ABCG4. Moreover, we show that ABCA1, ABCA7, and ABCG1 antibodies decrease cholesterol efflux from spermatozoa to lipid acceptors apoA-I and albumin and inhibit in vitro fertilization.
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Project description:The peroxisomal ATP-binding Cassette (ABC) transporters, which are called ABCD1, ABCD2 and ABCD3, are transmembrane proteins involved in the transport of various lipids that allow their degradation inside the organelle. Defective ABCD1 leads to the accumulation of very long-chain fatty acids and is associated with a complex and severe neurodegenerative disorder called X-linked adrenoleukodystrophy (X-ALD). Although the nucleotide-binding domain is highly conserved and characterized within the ABC transporters family, solid data are missing for the transmembrane domain (TMD) of ABCD proteins. The lack of a clear consensus on the secondary and tertiary structure of the TMDs weakens any structure-function hypothesis based on the very diverse ABCD1 mutations found in X-ALD patients. Therefore, we first reinvestigated thoroughly the structure-function data available and performed refined alignments of ABCD protein sequences. Based on the 2.85 ?Å resolution crystal structure of the mitochondrial ABC transporter ABCB10, here we propose a structural model of peroxisomal ABCD proteins that specifies the position of the transmembrane and coupling helices, and highlight functional motifs and putative important amino acid residues.
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Project description:Nitric oxide (NO) is an important regulator of renal transport processes. In the present study, we investigated the role of NO, produced by inducible NO synthase (iNOS), in the regulation of renal ATP-binding cassette (ABC) transporters in vivo during endotoxemia. Wistar-Hannover rats were injected with lipopolysaccharide (LPS(+)) alone or in combination with the iNOS inhibitor, aminoguanidine. Controls received detoxified LPS (LPS(-)). After LPS(+), proximal tubular damage and a reduction in renal function were observed. Furthermore, iNOS mRNA and protein, and the amount of NO metabolites in plasma and urine, increased compared to the LPS(-) group. Coadministration with aminoguanidine resulted in an attenuation of iNOS induction and reduction of renal damage. Gene expression of 20 ABC transporters was determined. After LPS(+), a clear up-regulation in Abca1, Abcb1/P-glycoprotein (P-gp), Abcb11/bile salt export pump (Bsep), and Abcc2/multidrug resistance protein (Mrp2) was found, whereas Abcc8 was down-regulated. Up-regulation of Abcc2/Mrp2 was accompanied by enhanced calcein excretion. Aminoguanidine attenuated the effects on transporter expression. Our data indicate that NO, produced locally by renal iNOS, regulates the expression of ABC transporters in vivo. Furthermore, we showed, for the first time, expression and subcellular localization of Abcb11/Bsep in rat kidney.
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Project description:BackgroundThe ATP-Binding Cassette (ABC) functional superfamily includes integral transmembrane exporters that have evolved three times independently, forming three families termed ABC1, ABC2 and ABC3, upon which monophyletic ATPases have been superimposed for energy-coupling purposes [e.g., J Membr Biol 231(1):1-10, 2009]. The goal of the work reported in this communication was to understand how the integral membrane constituents of ABC uptake transporters with different numbers of predicted or established transmembrane segments (TMSs) evolved. In a few cases, high resolution 3-dimensional structures were available, and in these cases, their structures plus primary sequence analyses allowed us to predict evolutionary pathways of origin.ResultsAll of the 35 currently recognized families of ABC uptake proteins except for one (family 21) were shown to be homologous using quantitative statistical methods. These methods involved using established programs that compare native protein sequences with each other, after having compared each sequence with thousands of its own shuffled sequences, to gain evidence for homology. Topological analyses suggested that these porters contain numbers of TMSs ranging from four or five to twenty. Intragenic duplication events occurred multiple times during the evolution of these porters. They originated from a simple primordial protein containing 3 TMSs which duplicated to 6 TMSs, and then produced porters of the various topologies via insertions, deletions and further duplications. Except for family 21 which proved to be related to ABC1 exporters, they are all related to members of the previously identified ABC2 exporter family. Duplications that occurred in addition to the primordial 3 → 6 duplication included 5 → 10, 6 → 12 and 10 → 20 TMSs. In one case, protein topologies were uncertain as different programs gave discrepant predictions. It could not be concluded with certainty whether a 4 TMS ancestral protein or a 5 TMS ancestral protein duplicated to give an 8 or a 10 TMS protein. Evidence is presented suggesting but not proving that the 2TMS repeat unit in ABC1 porters derived from the two central TMSs of ABC2 porters. These results provide structural information and plausible evolutionary pathways for the appearance of most integral membrane constituents of ABC uptake transport systems.ConclusionsAlmost all integral membrane uptake porters of the ABC superfamily belong to the ABC2 family, previously established for exporters. Most of these proteins can have 5, 6, 10, 12 or 20 TMSs per polypeptide chain. Evolutionary pathways for their appearance are proposed.
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