ABC50 Promotes Translation Initiation in Mammalian Cells

Abstract

ABC50 is an ATP-binding cassette (ABC) protein, which, unlike most ABC proteins, does not possess membrane-spanning domains. ABC50 interacts with eukaryotic initiation factor 2 (eIF2), which plays a key role in translation initiation and its control. ABC50 binds to ribosomes, and this interaction requires both the N-terminal domain and at least one ABC domain. Knockdown of ABC50 by RNA interference impaired translation of both cap-dependent and -independent reporters, consistent with a positive role for ABC50 in the function of eIF2, which is required for both types of translation initiation. Mutation of the Walker box A or B motifs in both ABC regions of ABC50 yielded a mutant protein that exerted a dominant-interfering phenotype with respect to protein synthesis and translation initiation. Importantly, although dominant-interfering mutants of ABC50 impaired cap-dependent translation, translation driven by certain internal ribosome entry segments was not inhibited. ABC50 is located in the cytoplasm and nucleoplasm but not in the nucleolus. Thus, ABC50 is not likely to be directly involved in early ribosomal biogenesis, unlike some other ABC proteins. Taken together, the present data show that ABC50 plays a key role in translation initiation and has functions that are distinct from those of other non-membrane ABC proteins.

A single intact ATPase site of the ABC transporter BtuCD drives 5% transport activity yet supports full in vivo vitamin B 12 utilization

“…We find that, in a membrane environment, the ATPase sites of BtuCD are highly cooperative with a Hill coefficient of 2. We also find that, when one of the ATPase sites is inactive, ATP hydrolysis and vitamin B 12 transport by BtuCD is reduced by 95%. These exact features are also shared by the archetypical type I maltose ABC transporter.…”

“…These exact features are also shared by the archetypical type I maltose ABC transporter. Remarkably, mutants that have lost 95% of their ATPase and transport capabilities still retain the ability to fully use vitamin B 12 in vivo. The results demonstrate that, despite the many differences between type I and type II ABC transporters, the fundamental mechanism of ATP hydrolysis remains conserved.…”

“…From bacteria to humans, they participate in processes such as cancer and bacterial multidrug resistance, antigen presentation, signal transduction, DNA repair, translation, cell division, homeostasis maintenance, detoxification, nutrient import, and antiviral defense (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Hydrolyzing ATP to drive transport, ABC transporters shuttle cargo molecules to and fro the various cellular compartments, through the impermeable barriers of cell membranes.…”

“…The many mechanistic differences between type I and type II ABC transporters raise the question whether in respect to ATP hydrolysis the two subtypes are similar or different. We have addressed this question by studying the Escherichia coli vitamin B 12 type II ABC transporter BtuCD. We have constructed and purified a series of BtuCD variants where both, one, or none of the ATPase sites were rendered inactive by mutation.…”

Ligand-gated Ion Channels

“…They are associated with cellular export of sterols and phospholipids, as well as exogenous drugs (ABCG2). A further group of ABC transporter-like proteins have been identified to lack membrane spanning regions and are not believed to be functional transporters, but appear to have a role in protein translation Paytubi et al, 2009): ABCE1 (ENSG00000164163, also known as OABP or 2′-5′ oligoadenylate-binding protein); ABCF1 (ENSG00000204574, also known as ABC50 or TNF-a-stimulated ABC protein); ABCF2 (ENSG00000033050, also known as iron-inhibited ABC transporter 2) and ABCF3 (ENSG00000161204).…”