SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator

SUR1 is an ATP-binding cassette (ABC) transporter with a novel function. In contrast to other ABC proteins, it serves as the regulatory subunit of an ion channel. The ATP-sensitive (KATP) channel is an octameric complex of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits, and it links cell metabolism to electrical activity in many cell types. ATPase activity at the nucleotide-binding domains of SUR results in an increase in KATP channel open probability. Conversely, ATP binding to Kir6.2 closes the channel. Metabolic regulation is achieved by the balance between these two opposing effects. Precisely how SUR1 talks to Kir6.2 remains unclear, but recent studies have identified some residues and domains that are involved in both physical and functional interactions between the two proteins. The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes. This paper reviews recent data on the regulation of Kir6.2 by SUR1 and considers the molecular mechanisms by which SUR1 mutations produce disease

VEGFA, B, C: Implications of the C-terminal sequence variations for the interaction with neuropilins

Vascular endothelial growth factors (VEGFs) are the key regulators of blood and lymphatic vessels’ formation and function. Each of the proteins from the homologous family VEGFA, VEGFB, VEGFC and VEGFD employs a core cysteine-knot structural domain for the specific interaction with one or more of the cognate tyrosine kinase receptors. Additional diversity is exhibited by the involvement of neuropilins–transmembrane co-receptors, whose b1 domain contains the binding site for the C-terminal sequence of VEGFs. Although all relevant isoforms of VEGFs that interact with neuropilins contain the required C-terminal Arg residue, there is selectivity of neuropilins and VEGF receptors for the VEGF proteins, which is reflected in the physiological roles that they mediate. To decipher the contribution made by the C-terminal sequences of the individual VEGF proteins to that functional differentiation, we determined structures of molecular complexes of neuropilins and VEGF-derived peptides and examined binding interactions for all neuropilin-VEGF pairs experimentally and computationally. While X-ray crystal structures and ligand-binding experiments highlighted similarities between the ligands, the molecular dynamics simulations uncovered conformational preferences of VEGF-derived peptides beyond the C-terminal arginine that contribute to the ligand selectivity of neuropilins. The implications for the design of the selective antagonists of neuropilins’ functions are discussed

The ATPase activities of sulfonylurea receptor 2A and sulfonylurea receptor 2B are influenced by the C-terminal 42 amino acids

Unusually among ATP-binding cassette proteins, the sulfonylurea receptor (SUR) acts as a channel regulator. ATP-sensitive potassium channels are octameric complexes composed of four pore-forming Kir6.2 subunits and four regulatory SUR subunits. Two different genes encode SUR1 (ABCC8) and SUR2 (ABCC9), with the latter being differentially spliced to give SUR2A and SUR2B, which differ only in their C-terminal 42 amino acids. ATP-sensitive potassium channels containing these different SUR2 isoforms are differentially modulated by MgATP, with Kir6.2/SUR2B being activated more than Kir6.2/SUR2A. We show here that purified SUR2B has a lower ATPase activity and a 10-fold lower K m for MgATP than SUR2A. Similarly, the isolated nucleotide-binding domain (NBD) 2 of SUR2B was less active than that of SUR2A. We further found that the NBDs of SUR2B interact, and that the activity of full-length SUR cannot be predicted from that of either the isolated NBDs or NBD mixtures. Notably, deletion of the last 42 amino acids from NBD2 of SUR2 resulted in ATPase activity resembling that of NBD2 of SUR2A rather than that of NBD2 of SUR2B: this might indicate that these amino acids are responsible for the lower ATPase activity of SUR2B and the isolated NBD2 of SUR2B. We suggest that the lower ATPase activity of SUR2B may result in enhanced duration of the MgADP-bound state, leading to channel activation. © 2010 FEBS

Small Molecule Neuropilin‑1 Antagonists Combine Antiangiogenic and Antitumor Activity with Immune Modulation through Reduction of Transforming Growth Factor Beta (TGFβ) Production in Regulatory T‑Cells

We report the design, synthesis, and biological evaluation of some potent small-molecule neuropilin-1 (NRP1) antagonists. NRP1 is implicated in the immune response to tumors, particularly in Treg cell fragility, required for PD1 checkpoint blockade. The design of these compounds was based on a previously identified compound EG00229. The design of these molecules was informed and supported by X-ray crystal structures. Compound <b>1</b> (EG01377) was identified as having properties suitable for further investigation. Compound <b>1</b> was then tested in several in vitro assays and was shown to have antiangiogenic, antimigratory, and antitumor effects. Remarkably, <b>1</b> was shown to be selective for NRP1 over the closely related protein NRP2. In purified Nrp1⁺, FoxP3⁺, and CD25⁺ populations of Tregs from mice, <b>1</b> was able to block a glioma-conditioned medium-induced increase in TGFβ production. This comprehensive characterization of a small-molecule NRP1 antagonist provides the basis for future in vivo studies

Small Molecule Neuropilin‑1 Antagonists Combine Antiangiogenic and Antitumor Activity with Immune Modulation through Reduction of Transforming Growth Factor Beta (TGFβ) Production in Regulatory T‑Cells

We report the design, synthesis, and biological evaluation of some potent small-molecule neuropilin-1 (NRP1) antagonists. NRP1 is implicated in the immune response to tumors, particularly in Treg cell fragility, required for PD1 checkpoint blockade. The design of these compounds was based on a previously identified compound EG00229. The design of these molecules was informed and supported by X-ray crystal structures. Compound <b>1</b> (EG01377) was identified as having properties suitable for further investigation. Compound <b>1</b> was then tested in several in vitro assays and was shown to have antiangiogenic, antimigratory, and antitumor effects. Remarkably, <b>1</b> was shown to be selective for NRP1 over the closely related protein NRP2. In purified Nrp1⁺, FoxP3⁺, and CD25⁺ populations of Tregs from mice, <b>1</b> was able to block a glioma-conditioned medium-induced increase in TGFβ production. This comprehensive characterization of a small-molecule NRP1 antagonist provides the basis for future in vivo studies