Dinámica estructural entre la conformación abierta y cerrada del canal KATP en células pancreáticas / Structural dynamics between the open and closed conformations of the KATP channel in pancreatic cells

INTRODUCCIÓN: el canal de Potasio sensible a ATP (canal KATP) regula la producción de Insulina por células ß pancreáticas. La Glibenclamida (GBM) (fármaco antidiabético) y el ATP actúan como inhibidores de este canal, mientras que el ADP lo activa. El canal KATP es un octámero constituido por 4 subunidades centrales Kir6.2 que forman el poro y 4 subunidades externas de regulación SUR1. OBJETIVO: determinar la dinámica estructural entre las conformaciones abierta y cerrada del canal KATP en células pancreáticas. MÉTODO: análisis estructural comparativo de diferentes estructuras cristalográficas del canal KATP de células pancreáticas humanas empleando el software Chimera v1.11.2 RESULTADOS: La subunidad Kir6.2 presenta un dominio de unión a PIP2 (activador), una Hélice Interfacial (IFH) y un dominio N-terminal (KNtp). Por otro lado, la subunidad SUR1 que contiene el sitio de unión a la GBM, tiene 2 Dominios de Unión a Nucleótidos (NBD1/2), un bucle M5-Lh1 y un Motivo de Lazo formado por la interface entre el Dominio Trans-membrana 0 y el Bucle 0 (TMD0-L0). Los resultados del análisis dinámico estructural mediante herramientas bioinformáticas, indican que estas regiones participan activamente en los cambios conformacionales que dan lugar al cierre (inhibición) o apertura (activación) de este canal. CONCLUSIÓN: El estudio de la dinámica de activación e inhibición de los canales KATP es imprescindible para la evaluación, descubrimiento y/o diseño de nuevos compuestos naturales, que como la GBM, puedan promover la secreción de Insulina para coadyuvar o mejorar el tratamiento de pacientes diabéticos.

INTRODUCTION: the ATP-sensitive Potassium channel (KATP channel) regulates insulin production by pancreatic ß cells. Glibenclamide (GBM) (antidiabetic drug) and ATP act as inhibitors of this channel, while ADP activates it. The KATP channel is an octamer consisting of 4 central Kir6.2 subunits that form the pore and 4 external regulation subunits SUR1. OBJECTIVE: to determine the structural dynamics between the open and closed conformations of the KATP channel in pancreatic cells. METHOD: comparative structural analysis of different crystallographic structures of the KATP channel of human pancreatic cells using Chimera v1.11.2. RESULTS: the Kir6.2 subunit has a PIP2 binding domain (activator), an Interfacial Helix (IFH) and an N-terminal domain (KNtp). On the other hand, the SUR1 subunit that contains the GBM binding site, has 2 Nucleotide Binding Domains (NBD1/2), an M5-Lh1 loop and a Lasso Motif formed by the interface between the Trans-membrane Domain 0 and Loop 0 (TMD0-L0). The results of the dynamic structural analysis using bioinformatics tools indicate that these regions participate actively in the conformational changes that lead to the closure (inhibition) or opening (activation) of this channel. CONCLUSION: the study of the dynamics of activation and inhibition of the KATP channels is essential for the evaluation, discovery and/or design of new natural compounds, which like GBM, can promote insulin secretion to aid or improve the treatment of diabetic patients.

Elucidation of the Inhibitory Effect of Phytochemicals with Kir6.2 Wild-Type and Mutant Models Associated in Type-1 Diabetes through Molecular Docking Approach

Among all serious diseases globally, diabetes (type 1 and type 2) still poses a major challenge to the world population. Several target proteins have been identified, and the etiology causing diabetes has been reasonably well studied. But, there is still a gap in deciding on the choice of a drug, especially when the target is mutated. Mutations in the KCNJ11 gene, encoding the kir6.2 channel, are reported to be associated with congenital hyperinsulinism, having a major impact in causing type 1 diabetes, and due to the lack of its 3D structure, an attempt has been made to predict the structure of kir6.2, applying fold recognition methods. The current work is intended to investigate the affinity of four phytochemicals namely, curcumin (Curcuma longa), genistein (Genista tinctoria), piperine (Piper nigrum), and pterostilbene (Vitis vinifera) in a normal as well as in a mutant kir6.2 model by adopting a molecular docking methodology. The phytochemicals were docked in both wild and mutated kir6.2 models in two rounds: blind docking followed by ATP-binding pocket-specific docking. From the binding pockets, the common interacting amino acid residues participating strongly within the binding pocket were identified and compared. From the study, we conclude that these phytochemicals have strong affinity in both the normal and mutant kir6.2 model. This work would be helpful for further study of the phytochemicals above for the treatment of type 1 diabetes by targeting the kir6.2 channel.

Neonatal Diabetes Caused by Activating Mutations in the Sulphonylurea Receptor

Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic beta-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory subunit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment.

Increased Expression of ATP-sensitive K+ Channels Improves the Right Ventricular Tolerance to Hypoxia in Rabbit Hearts

ATP-sensitive K+ channels (KATP) are major component of preventing ischemia-reperfusion injury. However, there is little information regarding to the expressional difference of K(ATP) and its function between left and right ventricles. In this study, we measured the lactate dehydrogenase release of rabbit heart slices in vitro and determined the difference of the K(ATP) expression at the both ventricles by measuring the level of K(ATP)-forming Kir6.2 (OcKir6.2) mRNA using in situ hybridization. The hearts were preconditioned with 15 min hypoxia and reoxygenated for 15 min before a hypoxic period of 60 min, followed by reoxygenation for 180 min. With hypoxic preconditioning (100% N2) with 15 min, left ventricles (LV) showed higher release of LDH comparing with right ventricles (RV). Adding KATP blocker glibenclamide (10 microM) prior to a hypoxic period of 60 min, hypoxic preconditioning effect of RV was more abolished than LV. With in situ hybridization, the optical density of OcKir6.2 was higher in RV. Therefore, we suggest that different K(ATP) expression between LV and RV is responsible for the different response to hypoxia and hypoxic preconditioning of rabbit hearts.

Expression of pancreatic Kir6.2 in diabetes rats and the intervention of astragalus polysaccharide at different doses / 国际外科学杂志

Objective To investigate the influence of astragalus polysaccharide administration on the the expression of pancreatic Kir6.2 in diabetes rats.Methods Wistar rats were induced diabetes mellitus,then divided into model group,control group,low dose group,and high dose group randomly.After OGTT of them were observed,determination of the Kir6.2 mRNA and protein expression levels in pancreas was performed by RT-PCR and Western blotting.Results The expression of Kir6.2 in model group decreased significantly,and the expressions of Kir6.2 in low dose and hish dose groups were higher than the model group (P<0.05).Conclusion Astragalus polysaccharide displayed up-regulation to the expression of pancreatic Kir6.2.which may be a mechanism on reducing blood glucose.

The Association Study of Kir6.2 E23K Polymorphism and Fat Distribution in Koreans / 체질인류학회지

Obesity is caused by interactions of energy consumption, amount of food intake, physical activity and etc, and these elements are influenced by genetic factors. Obesity related genes which have been known by now are over 200. One of these is Kir6.2 which forms the pore region of K(ATP) channel, and genetic variation of which may result in altered beta-cell electrical activity, insulin secretion, glucose homeostasis, and increased susceptibility to type 2 diabetes. Therefore, the purpose of this study was to examine the relationship between Kir6.2 E23K polymorphism and fat distribution or metabolic profiles in Korean. A total of 164 patients who visited Dongsan Medical Center Obesity Clinic from February 2004 to December 2005, were enrolled in this study. Screening for Kir6.2 polymorphism carried out by PCR-RFLP analyses. We divided this group into three groups E/E, E/K, K/K. Serum lipid and blood glucose were measured by autoanalyzer. Visceral fat amount and subcutaneous fat by abdominal CT, total fat mass by DEXA were measured. The subjects of E/E, E/K, K/K genotypes were 24, 79, and 61, respectively. The results of ANOVA analysis was that subjects with the K/K genotypes had more visceral fat amount (P<0.05) and higher total cholesterol levels (P<0.05) than E/E subjects group. Visceral fat amount and serum total cholesterol were significantly different according to Kir6.2 E23K polymorphism. Therefore, Kir6.2 polymorphism may act on fat distribution in Koreans.

Sulfonylurea Therapy in Two Korean Patients with Insulin-treated Neonatal Diabetes due to Heterozygous Mutations of the KCNJ11 Gene Encoding Kir6.2

Permanent neonatal diabetes (PND) is a rare form of diabetes characterized by insulin-requiring hyperglycemia diagnosed within the first three months of life. In most cases, the causes are not known. Recently, mutations in the KCNJ11 gene encoding the Kir6.2 subunit of the ATP-sensitive K(+) channel have been described in patients with PND. We report the first two Korean cases with PND due to a lysineto- arginine substitution at position 170 (K179R) and a valine-to-methionine substitution at position 59 (V59M) mutations of KCNJ11 encoding Kir6.2, respectively. After several years of insulin therapy, these patients were managed by oral glibenclamide therapy at a daily dose of 0.8-0.9 mg/kg. Their basal c-peptide levels increased after one week of glibenclamide therapy, and one month later, the insulin and c-peptide levels were in the normal ranges without any episodes of hyper- or hypoglycemia. These cases demonstrate that oral sulfonylurea may be the treatment of choice in PND patients with KCNJ11 mutations even at a young age.

Involvement of ERK1/2 and JNK Pathways in 17beta-estradiol Induced Kir6.2 and SK2 Upregulation in Rat Osteoblast-like Cells

The functional expression of potassium (K+) channels has electrophysiologically been studied in bone cells from several species, however, their identity and regulation of gene expressions in bone cells are not well known. In the present study, to investigate how K+ channel expressions are regulated by estrogen, we measured changes of transcript levels of various Ca2+-activated (K(Ca)) and ATP-sensitive K+ channels in rat osteoblastic ROS 17/2.8 cells after treatment with estrogen. Application of 17beta-estradiol (E2) for 24 h and 48 h increased mRNA and protein expressions of inwardly rectifying K+ channel (Kir) 6.2 and type 2 small conductance K(Ca) channel (SK2), respectively. Combined treatment of cells with 17beta-E2 and ICI 182,780, a pure antiestrogen, suppressed 17beta-E2-induced alterations of SK2 and Kir6.2 mRNA levels. In addition, treatment of cells with U0126, a specific inhibitor of extracellular receptor kinases (ERK)1/2, and SP600125, a specific inhibitor of c-jun N-terminal kinase (JNK) blocked the enhancing effects of 17beta-E2 on SK2 and Kir6.2 protein expressions. On the other hand, blocking of p38 mitogen-activated protein kinase had no effect. Taken together, these results indicate that 17beta-E2 modulates SK2 and Kir6.2 expressions through the estrogen receptor, involving ERK1/2 and JNK activations.