Hyperinsulinism-Causing Mutations Cause Multiple Molecular Defects in SUR1 NBD1

The ATP-bound inward-open conformation of ABCC4 reveals asymmetric ATP binding for substrate transport

The multidrug resistance-associated protein (MRP) ABCC4 facilitates substrate transport across the cytoplasmic membrane, crucial for normal physiology and mediating multidrug resistance in tumor cells. Despite intensive studies on MRPs, ABCC4's transport mechanism remains incompletely understood. In this study, we unveiled an inward-open conformation with an ATP bound to degenerate NBD1. Additionally, we captured the structure with both ATP and substrate co-bound in the inward-open state. Our findings uncover the asymmetric ATP binding in ABCC4 and provide insights into substrate binding and transport mechanisms. ATP binding to NBD1 is parallel to substrate binding to ABCC4, and is a prerequisite for ATP-bound NBD2-induced global conformational changes. Our findings shed new light on targeting ABCC4 in combination with anticancer therapy.

Structure of Ycf1p reveals the transmembrane domain TMD0 and the regulatory region of ABCC transporters

ATP binding cassette (ABC) proteins typically function in active transport of solutes across membranes. The ABC core structure is composed of two transmembrane domains (TMD1 and TMD2) and two cytosolic nucleotide binding domains (NBD1 and NBD2). Some members of the C-subfamily of ABC (ABCC) proteins, including human multidrug resistance proteins (MRPs), also possess an N-terminal transmembrane domain (TMD0) that contains five transmembrane α-helices and is connected to the ABC core by the L0 linker. While TMD0 was resolved in SUR1, the atypical ABCC protein that is part of the hetero-octameric ATP-sensitive K+ channel, little is known about the structure of TMD0 in monomeric ABC transporters. Here, we present the structure of yeast cadmium factor 1 protein (Ycf1p), a homolog of human MRP1, determined by electron cryo-microscopy (cryo-EM). A comparison of Ycf1p, SUR1, and a structure of MRP1 that showed TMD0 at low resolution demonstrates that TMD0 can adopt different orientations relative to the ABC core, including a ∼145° rotation between Ycf1p and SUR1. The cryo-EM map also reveals that segments of the regulatory (R) region, which links NBD1 to TMD2 and was poorly resolved in earlier ABCC structures, interacts with the L0 linker, NBD1, and TMD2. These interactions, combined with fluorescence quenching experiments of isolated NBD1 with and without the R region, suggest how posttranslational modifications of the R region modulate ABC protein activity. Mapping known mutations from MRP2 and MRP6 onto the Ycf1p structure explains how mutations involving TMD0 and the R region of these proteins lead to disease.

Intrinsically disordered regions regulate the activities of ATP binding cassette transporters

ATP binding cassette (ABC) proteins are a large family of membrane proteins present in all kingdoms of life. These multi-domain proteins are comprised, at minimum, of two membrane-spanning domains (MSD1, MSD2) and two cytosolic nucleotide binding domains (NBD1, NBD2). ATP binding and hydrolysis at the NBDs enables ABC proteins to actively transport solutes across membranes, regulate activities of other proteins, or function as channels. Like most eukaryotic membrane proteins, ABC proteins contain intrinsically disordered regions (IDRs). These conformationally dynamic regions in ABC proteins possess residual structure, are sites of phosphorylation, and mediate protein-protein interactions. Here, we review the role of IDRs in regulating ABC protein activity.

Analysis on the pathogenic genes of 60 Chinese children with congenital hyperinsulinemia

This study aims to summarize and analyze the clinical manifestations, genetic characteristics, treatment modalities and long-term prognosis of congenital hyperinsulinemia (CHI) in Chinese children. Sixty children with CHI, who were treated at Beijing Children's Hospital from January 2014 to August 2017, and their families, were selected as subjects. The CHI-related causative genes in children were sequenced and analyzed using second-generation sequencing technology. Furthermore, the genetic pathogenesis and clinical characteristics of Chinese children with CHI were explored. Among the 60 CHI children, 27 children (27/60, 45%) carried known CHI-related gene mutations: 16 children (26.7%) carried ABCC8 gene mutations, seven children (11.7%) carried GLUD1 gene mutations, one child carried GCK gene mutations, two children carried HNF4α gene mutations and one child carried HADH gene mutations. In these 60 patients, 8 patients underwent 18F-L-DOPA PET scan for the pancreas, and five children were found to be focal type. The treatment of diazoxide was ineffective in these five patients, and hypoglycemia could be controlled after receiving partial pancreatectomy. Conclusions: ABCC8 gene mutation is the most common cause of CHI in Chinese children. The early genetic analysis of children's families has an important guiding significance for treatment planning and prognosis assessment.

Phosphorylation Alters the Residual Structure and Interactions of the Regulatory L1 Linker Connecting NBD1 to the Membrane-Bound Domain in SUR2B

ATP-sensitive potassium (K_ATP) channels in vascular smooth muscle are comprised of four pore-forming Kir6.1 subunits and four copies of the sulfonylurea receptor 2B (SUR2B), which acts as a regulator of channel gating. Recent electron cryo-microscopy (cryo-EM) structures of the pancreatic K_ATP channel show a central Kir6.2 pore that is surrounded by the SUR1 subunits. Mutations in the L1 linker connecting the first membrane-spanning domain and the first nucleotide binding domain (NBD1) in SUR2B cause cardiac disease; however, this part of the protein is not resolved in the cryo-EM structures. Phosphorylation of the L1 linker, by protein kinase A, disrupts its interactions with NBD1, which increases the MgATP affinity of NBD1 and K_ATP channel gating. To elucidate the mode by which the L1 linker regulates K_ATP channels, we have probed the effects of phosphorylation on its structure and interactions using nuclear magnetic resonance (NMR) spectroscopy and other techniques. We demonstrate that the L1 linker is an intrinsically disordered region of SUR2B but possesses residual secondary and compact structure, both of which are disrupted with phosphorylation. NMR binding studies demonstrate that phosphorylation alters the mode by which the L1 linker interacts with NBD1. The data show that L1 linker residues with the greatest α-helical propensity also form the most stable interaction with NBD1, highlighting a hot spot within the L1 linker. This hot spot is the site of disease-causing mutations and is associated with other processes that regulate K_ATP channel gating. These data provide insights into the mode by which the phospho-regulatory L1 linker regulates K_ATP channels.