Unraveling the allosteric inhibition mechanism of PTP1B by free energy calculation based on umbrella sampling.

Protein tyrosine phosphatase 1B (PTP1B) is a promising target for the treatment of obesity and type II diabetes. Allosteric inhibitors can stabilize an active conformation of PTP1B by hindering the conformational transition of the WPD loop of PTP1B from the open to the closed state. Here, the umbrella sampling molecular dynamics (MD) simulations were employed to compute the reaction path of the conformational transition of PTP1B, and the snapshots extracted from the MD trajectory were clustered into 58 conformational groups based on the key conformational parameter. Then, the impact of the conformational change of the WPD loop on the interactions between the allosteric site of PTP1B and an allosteric inhibitor BB3 was explored by using the MM/GBSA binding free energy calculations and free energy decomposition analysis. The simulation results show that the binding free energy of BB3 increases gradually from the open to the closed conformation of the WPD loop, providing the molecular mechanism of allosteric inhibition. Correlation analysis of the different energy terms indicates that the allosteric inhibitor with more negative van der Waals contribution cannot only exhibit stronger binding affinity but also hinder the swing of the WPD loop more effectively. Besides, it is found that the energy contribution of Lys292 in the α7 helix undergoes significant change, which reveals that Lys292 is not only the key residue for ligand binding but also plays an important role in hindering the conformational change of the WPD loop.

Expression and significance of aquaporin-4 in thyroid carcinoma.

OBJECTIVE: To investigate the expression of aquaporin-4 (AQP4) in thyroid carcinoma (TC) and explore its clinical significance. MATERIALS AND METHODS: The formalin-fixed paraffin-embedded specimens including 275 TC cancer tissues, 258 corresponding paracancerous thyroid tissues and their clinicopathologic data were retrospectively analyzed. Immunohistochemical EnVision two-step method was used to detect the expression of AQP4 in the cancer tissues and adjacent thyroid tissues, and its clinical significance was analyzed. RESULTS: AQP4 could be expressed in both TC cancer tissues and paracancerous thyroid tissues. In TC cancer tissues, the positive expression rate was 99.3% (273/275), and the positive expression rate was 86.4% (223/258) in paracancerous thyroid tissues. The expression level of AQP4 in cancer tissues was significantly higher than that in paracancerous thyroid tissues, and the difference was statistically significant (P < 0.05). The positive expression rates of AQP4 in papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), medullary thyroid carcinoma (MTC) and undifferentiated thyroid carcinoma (UTC) were 99.2% (258/260), 100.0% (6/6), 100.0% (6/6) and 100.0% (3/3), respectively and there was little difference in different types of TC. Analysis of relationship between expression level of AQP4 in 275 TC cancer tissues and 260 PTC cancer tissues and clinicopathologic characteristics of patients was not significant correlation (P > 0.05). Among the 275 patients, one (0.4%, 1/275) was diagnosed as neuromyelitis optica spectrum disorder (NMOSD) associated with TC. CONCLUSIONS: AQP4 is generally expressed in TC cancer tissues and paracancerous thyroid tissues. Expression level of AQP4 in cancer tissues was significantly higher than that in paracancerous thyroid tissue. Expression level of AQP4 in TC cancer tissues is not related to the clinicopathological characteristics of the patients. Paraneoplastic NMOSD caused by TC is rare, and whether its specific pathogenesis is related to the expression of AQP4 in TC still needs further study.