RESUMO
Intestinal fructose uptake is mainly mediated by glucose transporter 5 (GLUT5/SLC2A5). Its closest relative, GLUT7, is also expressed in the intestine but does not transport fructose. For rat Glut5, a change of glutamine to glutamic acid at codon 166 (p.Q166E) has been reported to alter the substrate-binding specificity by shifting Glut5-mediated transport from fructose to glucose. Using chimeric proteins of GLUT5 and GLUT7, here we identified amino acid residues of GLUT5 that define its substrate specificity. The proteins were expressed in NIH-3T3 fibroblasts, and their activities were determined by fructose radiotracer flux. We divided the human GLUT5 sequence into 26 fragments and then replaced each fragment with the corresponding region in GLUT7. All fragments that yielded reduced fructose uptake were analyzed further by assessing the role of individual amino acid residues. Various positions in the first extracellular loop, in the fifth, seventh, eighth, ninth, and tenth transmembrane domains (TMDs), and in the regions between the ninth and tenth TMDs and tenth and 11th TMDs were identified as being important for proper fructose uptake. Although the p.Q167E change did not render the human protein into a glucose transporter, molecular dynamics simulations revealed a drastic change in the dynamics and a movement of the intracellular loop connecting the sixth and seventh TMDs, which covers the exit of the ligand. Finally, we generated a GLUT7-GLUT5 chimera consisting of the N-terminal part of GLUT7 and the C-terminal part of GLUT5. Although this chimera was inactive, we demonstrate fructose transport after introduction of four amino acids derived from GLUT5.
Assuntos
Aminoácidos/fisiologia , Frutose/metabolismo , Proteínas Facilitadoras de Transporte de Glucose/metabolismo , Transportador de Glucose Tipo 5/metabolismo , Sequência de Aminoácidos/genética , Sequência de Aminoácidos/fisiologia , Animais , Proteínas Facilitadoras de Transporte de Glucose/química , Transportador de Glucose Tipo 5/química , Humanos , Camundongos , Células NIH 3T3 , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/fisiologia , Ratos , Proteínas Recombinantes de Fusão/metabolismo , Especificidade por SubstratoRESUMO
Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K(+) channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na(+), Cs(+), and dimethylammonium (DMA(+)), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels.
Assuntos
Canais de Cátion Regulados por Nucleotídeos Cíclicos/química , Canais de Cátion Regulados por Nucleotídeos Cíclicos/metabolismo , Ativação do Canal Iônico/fisiologia , Conformação Proteica , Sequência de Aminoácidos , Animais , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Cátions Monovalentes/metabolismo , Bovinos , Césio/metabolismo , Cristalografia por Raios X , Canais de Cátion Regulados por Nucleotídeos Cíclicos/genética , Feminino , Ativação do Canal Iônico/genética , Transporte de Íons/efeitos dos fármacos , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Mutação de Sentido Incorreto , Oócitos/metabolismo , Oócitos/fisiologia , Técnicas de Patch-Clamp , Homologia de Sequência de Aminoácidos , Sódio/metabolismo , Xenopus laevisRESUMO
Sodium-Galactose Transporter (SGLT) is a secondary active symporter which accumulates sugars into cells by using the electrochemical gradient of Na+ across the membrane. Previous computational studies provided insights into the release process of the two ligands (galactose and sodium ion) into the cytoplasm from the inward-facing conformation of Vibrio parahaemolyticus sodium/galactose transporter (vSGLT). Several aspects of the transport mechanism of this symporter remain to be clarified: (i) a detailed kinetic and thermodynamic characterization of the exit path of the two ligands is still lacking; (ii) contradictory conclusions have been drawn concerning the gating role of Y263; (iii) the role of Na+ in modulating the release path of galactose is not clear. In this work, we use bias-exchange metadynamics simulations to characterize the free energy profile of the galactose and Na+ release processes toward the intracellular side. Surprisingly, we find that the exit of Na+ and galactose is non-concerted as the cooperativity between the two ligands is associated to a transition that is not rate limiting. The dissociation barriers are of the order of 11-12 kcal/mol for both the ion and the substrate, in line with kinetic information concerning this type of transporters. On the basis of these results we propose a branched six-state alternating access mechanism, which may be shared also by other members of the LeuT-fold transporters.
Assuntos
Galactose/química , Galactose/metabolismo , Proteínas de Transporte de Sódio-Glucose/química , Proteínas de Transporte de Sódio-Glucose/metabolismo , Cinética , Simulação de Dinâmica Molecular , Sódio/química , Sódio/metabolismo , TermodinâmicaRESUMO
PURPOSE: Pancreatic ductal adenocarcinoma (PDAC) upregulates CD73, potentially contributing to immune surveillance evasion. Combining oleclumab (CD73 inhibitor) and durvalumab with chemotherapy may identify an effective treatment option. PATIENTS AND METHODS: Multicenter Phase 1b/2 randomized clinical trial in patients with metastatic PDAC, untreated (Cohort A) or previously received gemcitabine-based chemotherapy (Cohort B) (NCT03611556). During escalation, patients received oleclumab 1500 or 3000 mg, durvalumab 1500 mg, and gemcitabine plus nab-paclitaxel (GnP) (Cohort A; n=14) or modified FOLFOX (Cohort B; n=11). During expansion, Cohort A patients (n=170) were randomized to: GnP (Arm A1), oleclumab (recommended Phase 2 dose; RP2D) with GnP (Arm A2), or oleclumab (RP2D) with durvalumab plus GnP (Arm A3). Primary objectives were safety (escalation) and objective response rate (ORR) (expansion). Secondary objectives included progression-free survival (PFS) and overall survival (OS). RESULTS: During escalation, 1/11 patients from Cohort B (oleclumab 3000 mg) experienced two dose-limiting toxicities. Oleclumab RP2D was 3000 mg. During expansion, Grade ≥3 treatment-related adverse events occurred in 67.7% (42/62) of patients in A1, 73.7% (28/38) in A2, and 77.1% (54/70) in A3. ORR was 29.0%, 21.1%, and 32.9% in A1, A2, and A3, respectively (A1 vs A3; p=0.650). PFS (hazard ratio [HR]=0.72; 95% confidence interval [CI]: 0.47, 1.11) and OS (HR=0.75; 95% CI: 0.50, 1.13) were similar for A3 versus A1. Patients with high CD73 expression had improved PFS and OS in A3 versus A1, although this should be interpreted with caution. CONCLUSIONS: Although the safety profile was acceptable, this study did not meet its primary efficacy endpoint.
RESUMO
Mutations in the STK11 (LKB1) gene regulate resistance to PD-1/PD-L1 blockade. This study evaluated this association in patients with nonsquamous non-small cell lung cancer (NSCLC) enrolled in three phase I/II trials. STK11 mutations were associated with resistance to the anti-PD-L1 antibody durvalumab (alone/with the anti-CTLA4 antibody tremelimumab) independently of KRAS mutational status, highlighting STK11 as a potential driver of resistance to checkpoint blockade. Retrospective assessments of tumor tissue, whole blood, and serum revealed a unique immune phenotype in patients with STK11 mutations, with increased expression of markers associated with neutrophils (i.e., CXCL2, IL6), Th17 contexture (i.e., IL17A), and immune checkpoints. Associated changes were observed in the periphery. Reduction of STAT3 in the tumor microenvironment using an antisense oligonucleotide reversed immunotherapy resistance in preclinical STK11 knockout models. These results suggest that STK11 mutations may hinder response to checkpoint blockade through mechanisms including suppressive myeloid cell biology, which could be reversed by STAT3-targeted therapy. SIGNIFICANCE: Patients with nonsquamous STK11-mutant (STK11mut) NSCLC are less likely than STK11 wild-type (STK11wt) patients to respond to anti-PD-L1 ± anti-CTLA4 immunotherapies, and their tumors show increased expression of genes and cytokines that activate STAT3 signaling. Preclinically, STAT3 modulation reverses this resistance, suggesting STAT3-targeted agents as potential combination partners for immunotherapies in STK11mut NSCLC.This article is highlighted in the In This Issue feature, p. 2659.
Assuntos
Carcinoma Pulmonar de Células não Pequenas , Neoplasias Pulmonares , Quinases Proteína-Quinases Ativadas por AMP , Anticorpos Monoclonais , Anticorpos Monoclonais Humanizados , Antígeno B7-H1/metabolismo , Carcinoma Pulmonar de Células não Pequenas/tratamento farmacológico , Carcinoma Pulmonar de Células não Pequenas/genética , Carcinoma Pulmonar de Células não Pequenas/patologia , Humanos , Neoplasias Pulmonares/tratamento farmacológico , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patologia , Mutação , Proteínas Serina-Treonina Quinases/genética , Estudos Retrospectivos , Fator de Transcrição STAT3/genética , Fator de Transcrição STAT3/metabolismo , Microambiente TumoralRESUMO
The recent Vibrio parahaemolyticus sodium/galactose (vSGLT) symporter crystal structure captures the protein in an inward-facing substrate-bound conformation, with the sodium ion placed, by structural alignment, in a site equivalent to the Na2 site of the leucine transporter (LeuT). A recent study, based on molecular dynamics simulations, showed that the sodium ion spontaneously leaves its initial position diffusing outside vSGLT, toward the intracellular space. This suggested that the crystal structure corresponds to an ion-releasing state of the transporter. Here, using metadynamics, we identified a more stable Na(+) binding site corresponding to a putative ion-retaining state of the transporter. In addition, our simulations, consistently with mutagenesis studies, highlight the importance of D189 that, without being one of the Na(+)-coordinating residues, regulates its binding/release.