SummaryAn essential feature of many site-specific recombination systems is their ability to regulate the direction and topology of recombination. Resolvases from the serine recombinase family assemble an interwound synaptic complex that harnesses negative supercoiling to drive the forward reaction and promote recombination between properly oriented sites. To better understand the interplay of catalytic and regulatory functions within these synaptic complexes, we have solved the structure of the regulatory site synapse in the Sin resolvase system. It reveals an unexpected synaptic interface between helix-turn-helix DNA-binding domains that is also highlighted in a screen for synapsis mutants. The tetramer defined by this interface provides the foundation for a robust model of the synaptic complex, assembled entirely from available crystal structures, that gives insight into how the catalytic activity of Sin and other serine recombinases may be regulated.
There are multiple proposed mechanisms for the pathophysiology of heart failure (HF) with preserved ejection fraction (HFpEF). We hypothesized that coronary microvascular dysfunction is common in these patients. In a prospective, observational study, patients undergoing cardiac catheterization with HFpEF [left ventricular (LV) ejection fraction ≥ 50% and with clinical HF] were compared with similar patients without HFpEF. Patients with ≥50% stenosis were excluded, and coronary flow reserve (CFR) and the index of microvascular resistance (IMR) were measured after adenosine administration using a guidewire, with CFR ≤ 2 and IMR ≥ 23 being abnormal. Baseline characteristics and CFR and IMR were compared in 30 HFpEF patients and 14 control subjects. Compared with control subjects, HFpEF patients were older (65.4 ± 9.6 vs. 55.1 ± 3.1 yr, P < 0.01), had higher numbers of comorbidities (4.4 ± 1.5 vs. 2.6 ± 1.9, P = 0.002), had higher median B-type natriuretic peptide [161 (interquartile range: 75-511) pg/dl vs. 37 (interquartile range: 18.5-111) pg/dl, P < 0.01], and had higher LV end-diastolic pressure (17.8 ± 4.2 vs. 8.4 ± 4.2, P < 0.01). HFpEF patients had lower CFR (2.55 ± 1.60 vs. 3.84 ± 1.89, P = 0.024) and higher IMR (26.7 ± 10.3 vs. 19.7 ± 9.7 units, P = 0.037) than control subjects. Most (71.4%) control subjects had normal coronary physiology, whereas 36.7% of HFpEF patients had both abnormal CFR and IMR and another 36.7% had either abnormal CFR or IMR. In conclusion, this is the first study that has reported invasively determined CFR and IMR in HFpEF patients. We demonstrated the presence of four distinct coronary physiology groups in HFpEF patients. Investigation into the potential mechanisms for these findings is needed. NEW & NOTEWORTHY In this prospective observational study of patients with heart failure with preserved ejection fraction (HFpEF), we found that patients with HFpEF had more abnormalities of coronary flow and resistance than asymptomatic control patients, indicating that coronary microvascular dysfunction may play a role in the HFpEF disease process.
IL-1R-associated kinase (IRAK) 4 is an essential component of innate immunity. IRAK-4 deficiency in mice and humans results in severe impairment of IL-1 and TLR signaling. We have solved the crystal structure for the death domain of Mus musculus IRAK-4 to 1.7 Å resolution. This is the first glimpse of the structural details of a mammalian IRAK family member. The crystal structure reveals a six-helical bundle with a prominent loop, which among IRAKs and Pelle, a Drosophila homologue, is unique to IRAK-4. This highly structured loop contained between helices two and three, comprises an 11-aa stretch. Although innate immune domain recognition is thought to be very similar between Drosophila and mammals, this structural component points to a drastic difference. This structure can be used as a framework for future mutation and deletion studies and potential drug design.
Background Transcatheter aortic valve replacement (TAVR) is increasingly used to treat severe aortic stenosis. A frequent complication of TAVR is high‐grade or complete atrioventricular (AV) block requiring a permanent pacemaker (PPM). There are little data on the long‐term dependency on pacing after TAVR. The objective of this study was to determine the proportion of patients receiving a PPM for high‐grade or complete AV block after TAVR who remain dependent on the PPM in follow‐up and to determine any risk factors for, particularly the effect of postballoon dilation (PBD) on, pacemaker dependency. Methods Of 594 consecutive patients without prior PPM undergoing TAVR (81.9% balloon‐expandable, 18.1% self‐expandable valve), 67 (13.1%) received a PPM after TAVR. PPM dependency was defined as AV block with a ventricular escape rate of ≤ 40 beats/min. Patient and procedural characteristics were examined according to PPM dependency status. Results Of the 67 patients who received a PPM within 10 days after TAVR, 27/67 (40.3%) were dependent at first follow‐up and only 9/41 (21.9%) at 1 year. PPM dependency was more common after a self‐expanding valve (76.9% vs 31.5%, P < 0.01), in those who underwent PBD (66.7% vs 24.4%, P < 0.01), and in patients in persistent complete AV block at PPM implantation (62.5% vs 7.4%, P < 0.01). Conclusions Fewer than half of patients who receive a new PPM following TAVR are pacemaker dependent at early follow‐up (< 30 days). The use of self‐expanding valves and PBD are associated with a markedly increased risk of PPM dependency.
The use of NOAC therapy for AF in patients with bioprosthetic valves appears safe and effective in the occurrence of thromboembolic events, however, at the expense of increased bleeding. Larger studies are necessary to confirm these findings.
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