The mechanism of the reverse recovery-step, phosphate release, and actin activation of Dictyostelium myosin II.

The rate-limiting step of the myosin basal ATPase (i.e. in absence of actin) is assumed to be a post-hydrolysis swinging of the lever arm (reverse recovery step), that limits the subsequent rapid product release steps. However, direct experimental evidence for this assignment is lacking. To investigate the binding and the release of ADP and phosphate independently from the lever arm motion, two single tryptophan-containing motor domains of Dictyostelium myosin II were used. The single tryptophans of the W129+ and W501+ constructs are located at the entrance of the nucleotide binding pocket and near the lever arm, respectively. Kinetic experiments show that the rate-limiting step in the basal ATPase cycle is indeed the reverse recovery step, which is a slow equilibrium step (k(forward) = 0.05 s(-1), k(reverse) = 0.15 s(-1)) that precedes the phosphate release step. Actin directly activates the reverse recovery step, which becomes practically irreversible in the actin-bound form, triggering the power stroke. Even at low actin concentrations the power stroke occurs in the actin-attached states despite the low actin affinity of myosin in the pre-power stroke conformation

Enzyme Kinetics above Denaturation Temperature: A Temperature-Jump/Stopped-Flow Apparatus

We constructed a “temperature-jump/stopped-flow” apparatus that allows us to study fast enzyme reactions at extremely high temperatures. This apparatus is a redesigned stopped-flow which is capable of mixing the reactants on a submillisecond timescale concomitant with a temperature-jump even as large as 60°C. We show that enzyme reactions that are faster than the denaturation process can be investigated above denaturation temperatures. In addition, the temperature-jump/stopped-flow enables us to investigate at physiological temperature the mechanisms of many human enzymes, which was impossible until now because of their heat instability. Furthermore, this technique is extremely useful in studying the progress of heat-induced protein unfolding. The temperature-jump/stopped-flow method combined with the application of structure-specific fluorescence signals provides novel opportunities to study the stability of certain regions of enzymes and identify the unfolding-initiating regions of proteins. The temperature-jump/stopped-flow technique may become a breakthrough in exploring new features of enzymes and the mechanism of unfolding processes

Reversible movement of switch 1 loop of myosin determines actin interaction

The conserved switch 1 loop of P-loop NTPases is implicated as a central element that transmits information between the nucleotide-binding pocket and the binding site of the partner proteins. Recent structural studies have identified two states of switch 1 in G-proteins and myosin, but their role in the transduction mechanism has yet to be clarified. Single tryptophan residues were introduced into the switch 1 region of myosin II motor domain and studied by rapid reaction methods. We found that in the presence of MgADP, two states of switch 1 exist in dynamic equilibrium. Actin binding shifts the equilibrium towards one of the MgADP states, whereas ATP strongly favors the other. In the light of electron cryo-microscopic and X-ray crystallographic results, these findings lead to a specific structural model in which the equilibrium constant between the two states of switch 1 is coupled to the strength of the actin-myosin interaction. This has implications for the enzymatic mechanism of G-proteins and possibly P-loop NTPases in genera

Korai mentális teszt: az enyhe kognitív zavar szűrőtesztjének fejlesztése = Early Mental Test: Developing a Screening Test for Mild Cognitive Impairment

BACKGROUND AND PURPOSE: Mild cognitive impairment (MCI) is a heterogenous syndrome considered as a prodromal state of dementia with clinical importance in the early detection of Alzheimer's Disease. We are currently developing an MCI screening instrument, the Early Mental Test (EMT) suitable to the needs of primary care physicians. The present study describes the validation process of the 6.2 version of the test. METHODS: Only subjects (n = 132, female 95, male 37) over the age of 55 (mean age 69.2 years (SD = 6.59)) scoring at least 20 points on Mini-Mental State Examination (MMSE), mean education 11.17 years (SD = 3.86) were included in the study. The psychometric evaluation consisted of Alzheimer's Disease Assessment Scale Cognitive subscale (ADAS-Cog) and the 6.2 version of EMT. The statistical analyses were carried out using the 17.00 version of SPSS statistical package. RESULTS: The optimalised cut-off point was found to be 3.45 points with corresponding 69% sensitivity, 69% specificity and 69% accuracy measures. The Cronbach-alpha, that describes the internal consistence of the test was 0.667, which is higher as compared with the same category in the case of the ADAS-Cog (0.446). A weak negative rank correlation was found between the total score of EMT 6.2 and the age of probands (rs = -0.25, p = 0.003). Similarly, only a weak correlation was found between the education levels and the total score of EMT 6.2 (rs = 0.31, p < 0.001). Two of the subtests, the repeated delayed short-time memory and the letter fluency test with a motorical distraction task had significantly better power to separate MCI and control groups than the other subtests of the EMT. CONCLUSION: The 6.2 version of EMT is a fast and simple detector of MCI with a similar sensitivity-specificity profile to the MMSE, but this version of the test definitely needs further development

Learning Curve for Starting a Successful Single-Centre TAVR Programme with Multiple Devices: Early and Mid-Term Follow-Up

Aims: We report 30-day, 1-year, and 3-year outcomes for a new TAVR programme that used five different transcatheter heart valve (THV) systems. Methods: From 2014 to 2020, 122 consecutive patients with severe aortic stenosis (AS) received TAVR based on the Heart Team decision. Outcomes were analysed for the whole study population and in addition the first 63 patients (Cohort A, 2014 to 2019) were compared to the last 59 patients (Cohort B, 2019 to 2020). Outcomes included VARC-2 definitions and device performance assessed via transthoracic echocardiography by independent high-volume investigators. Results: The mean patient age was 77.9 ± 6.1 years old, and 48 (39.3%) were male. The mean logistic Euroscore II was 4.2 ± 4.5, and the mean STS score was 6.9 ± 4.68. The systems used were as follows: Medtronic Corevalve Evolute R/PRO (82 patients—67.2%); Abbott Portico (13—10.6%); Boston Scientific Lotus (10—8.2%); Meril Myval (11—9%); and Boston Scientific Neo Accurate (6—5%). Access was transfemoral (95.9% of patients); surgical cut down (18% vs. percutaneous 77.8%); subclavian (n = 2); trans-axillary (n = 2); and direct aorta (n = 1). VARC-2 outcomes were as follows: device success rate 97.5%; stroke rate 1.6%; major vascular complication 3.3%; permanent pacemaker implantation 12.4%. At discharge, the incidences of grade I and II aortic regurgitation were 39.95 and 55.5%, respectively. At one year, all-cause mortality was 7.4% without admissions for valve-related dysfunction. The 3-year all-cause mortality and all-stroke rates were 22.9% and 4.1%, respectively. Between the 1-year and 3-year follow-ups, valve-related dysfunction was detected in three patients; one had THV system endocarditis that led to death. There was a remarkable but statistically non-significant decrease in mortality from Cohort A to Cohort B [four (6.3%) vs. one patient (1.7%), p = 0.195] and major vascular complications occurred at a significantly higher rate in the Cohort B [zero (0%) vs. four (6.8% patient, p = 0.036)]. Overall, we found that using multiple devices was safe and allowed for a learning team to achieve a high device success rate from the beginning (97.5%). Conclusions: TAVR with different THV systems showed acceptable early and mid-term outcomes for survival, technical success, and valve-related adverse events in high-risk patients with significant AS, even in the learning curve phase