Abstract
The ABCG2 structure reveals the multidrug-binding pocket and suggests a multidrug transport mechanism.
Major finding: The ABCG2 structure reveals the multidrug-binding pocket and suggests a multidrug transport mechanism.
Approach: Single-particle cryo-electron microscopy revealed a high-resolution structure of ABCG2 in complex with 5D3.
Impact: The ABCG2 structure may guide design of inhibitors to block multidrug resistance.
ABCG2 is a constitutively expressed ATP-binding cassette transporter that can alter the pharmacokinetics of many drugs and has been shown to expel antitumor drugs from cancer cells, promoting multidrug resistance. Thus, ABCG2 represents a potential therapeutic target. However, understanding of the drug-binding pocket is limited, as only low-resolution structural data is available. Taylor, Manolaridis, Jackson, and colleagues used single-particle cryo-electron microscopy to obtain a high-resolution (3.8Å) structure of human ABCG2 in complex with two antigen-binding fragments of the inhibitory antibody 5D3. ABCG2 is a half-transporter comprised of a nucleotide-binding domain (NBD) and transmembrane domain fused to a polypeptide chain and forms homodimers to generate the functional form. The architecture of ABCG2 is similar to the related ABC transporters ABCG5/G8, but ABCG2 has an inward facing cavity that is not present in ABCG5/G8. Further, the C2 motif is located away from the NBD and the Walker-A motif, indicating that it is not directly involved in ATP binding to the canonical site as was previously proposed. Notably, binding of only one 5D3 fragment was required for inhibition of ABCG2 ATPase activity, supporting the possibility that a single 5D3 molecule can inhibit transport activity by clamping the ABCG2 monomers together to prevent the outward-facing conformation required for active transport. The ABCG2–5D3 structure had an inward-open conformation with a deep hydrophobic cavity that opens to the cytoplasm, comprising the multidrug binding pocket, which bound to two cholesterol molecules. Altogether, the structure suggests a mechanism by which ATP binding promotes closing of the NBD interface and a conversion from the substrate-bound inward-open conformation of ABCG2 to an outward-facing state that can release the substrate to the outside. These structural insights may guide structure-based drug design to potentially inhibit ABCG2 and block drug resistance.
Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at http://cancerdiscovery.aacrjournals.org/content/early/by/section.
RSS Feeds