Impact of Nonnative Interactions on the Binding Kinetics of Intrinsically Disordered p53 with MDM2: Insights from All-Atom Simulation and Markov State Model Analysis.

Intrinsically disordered proteins (IDPs) lack a well-defined tertiary structure but are essential players in various biological processes. Their ability to undergo a disorder-to-order transition upon binding to their partners, known as the folding-upon-binding process, is crucial for their function. One classical example is the intrinsically disordered transactivation domain (TAD) of the tumor suppressor protein p53, which quickly forms a structured α-helix after binding to its partner MDM2, with clinical significance for cancer treatment. However, the contribution of nonnative interactions between the IDP and its partner to the rapid binding kinetics, as well as their interplay with native interactions, is not well understood at the atomic level. Here, we used molecular dynamics simulation and Markov state model (MSM) analysis to study the folding-upon-binding mechanism between p53-TAD and MDM2. Our results suggest that the system progresses from the nascent encounter complex to the well-structured encounter complex and finally reaches the native complex, following an induced-fit mechanism. We found that nonnative hydrophobic and hydrogen bond interactions, combined with native interactions, effectively stabilize the nascent and well-structured encounter complexes. Among the nonnative interactions, Leu25p53-Leu54MDM2 and Leu25p53-Phe55MDM2 are particularly noteworthy, as their interaction strength is close to the optimum. Evidently, strengthening or weakening these interactions could both adversely affect the binding kinetics. Overall, our findings suggest that nonnative interactions are evolutionarily optimized to accelerate the binding kinetics of IDPs in conjunction with native interactions.

[Second trimester screening for trisomy 21 using ADAM12-S as a maternal serum marker].

OBJECTIVE: To investigate the value of a disintegrin and metalloproteinase 12 secreting form (ADAM12-S) as a maternal serum marker in second trimester screening for trisomy 21 (Down syndrome, DS), and to develop an appropriate prenatal DS screening protocol. METHODS: Serum samples were collected from 53 pregnant women carrying a trisomy 21 fetus and 621 pregnant women with matched gestational age and weight carrying a healthy fetus. ADAM12-S concentrations were determined with a time-resolved fluorescence immunoassay (TRFIA). Curve fitting by weighted regression and other statistical methods were conducted, and the model was optimized for prenatal trisomy 21 screening program in second trimester. ADAM12-S alone or in combination with other two- or three-combination test was selected as a serum marker for prenatal second-trimester screening of trisomy 21 by calculation of detection rate (DR) and false positive rate (FPR). RESULTS: By comparison, the median multiple of the median (MoM) value of ADAM12-S in DS pregnancy group was higher than that of the control group (P< 0.01). When FPR = 5%, the DR of ADAM12-S was 28.3%, and the positive and negative likelihood ratios were 5.66 and 0.75, respectively. The DR of three-combination test of ADAM12-S, alpha-fetoprotein (AFP) and free beta subunit of human chorionic gonadotropin (ß-HCG) has increased to 52.80% from 39.62% of the conventional two-combination test (AFP and free ß-HCG). For women with a risk between 1/300 and 1/1000 by two-combination test for DS, the DR has increased from 39.62% to 47.12%, but FPR only increased by 0.8% after adding ADAM12-S as a maternal serum marker. CONCLUSION: Considering the increased DR of pregnancies with a risk between 1/300 and 1/1000 in second trimester, ADAM12-S may provide a feasible maternal serum maker when combined with AFP and free ß-HCG. The cost-effectiveness ratio is reasonable.

Comparison of Sandstone Damage Measurements Based on Non-Destructive Testing.

Non-destructive testing (NDT) methods are an important means to detect and assess rock damage. To better understand the accuracy of NDT methods for measuring damage in sandstone, this study compared three NDT methods, including ultrasonic testing, electrical impedance spectroscopy (EIS) testing, computed tomography (CT) scan testing, and a destructive test method, elastic modulus testing. Sandstone specimens were subjected to different levels of damage through cyclic loading and different damage variables derived from five different measured parameters-longitudinal wave (P-wave) velocity, first wave amplitude attenuation, resistivity, effective bearing area and the elastic modulus-were compared. The results show that the NDT methods all reflect the damage levels for sandstone accurately. The damage variable derived from the P-wave velocity is more consistent with the other damage variables, and the amplitude attenuation is more sensitive to damage. The damage variable derived from the effective bearing area is smaller than that derived from the other NDT measurement parameters. Resistivity provides a more stable measure of damage, and damage derived from the acoustic parameters is less stable. By developing P-wave velocity-to-resistivity models based on theoretical and empirical relationships, it was found that differences between these two damage parameters can be explained by differences between the mechanisms through which they respond to porosity, since the resistivity reflect pore structure, while the P-wave velocity reflects the extent of the continuous medium within the sandstone.

[Prenatal genetic study of fetuses with congenital heart diseases].

OBJECTIVE: To investigate the genetic abnormalities of fetuses with congenital heart diseases (CHD), and to provide guidance for the management of pregnancy and genetic counseling. METHODS: Eighty-one fetuses with CHD detected by fetal echocardiography were analyzed by karyotyping after amniocentesis, cordocentesis or chorionic sampling. Then 22q11.2 deletion/duplication was detected by a competitive fluorescent multiplex short tandem repeat assay in 47 CHD fetuses without chromosomal abnormalities. With fluorescence in situ hybridization (FISH) using LSI dual color DNA probe, the deletion/duplication status was confirmed. RESULTS: Thirty-four of 81 CHD fetuses had chromosomal anomalies, and 1 of the 47 CHD fetuses without chromosomal anomalies had duplication at chromosome 22q11. The incidence of aneuploidy associated CHD was 43.2%. The rate of chromosomal anomalies is higher in the cases associated with extra-cardiac anomalies than in that with isolated CHD (64.5% versus 28.0%). In the 35 fetuses with chromosomal abnormalities, 19 (54.3%) were trisomy 18. CONCLUSION: Chromosomal abnormalities occurred in 43.2% of CHD cases and trisomy 18 is the most common aneuploidy. The likelihood of chromosomal anomaly increases when there is extracardiac involvement. Testing for the 22q11.2 microdeletion/duplication is recommended in all CHD fetuses without chromosomal anomalies. It is important for the further management of pregnancy and genetic counseling.