Bacterial shape is physically determined by the peptidoglycan cell wall. The cell-wall-synthesis machinery responsible for rod shape in Escherichia coli is the processive 'Rod complex'. Previously, cytoplasmic MreB filaments were thought to govern formation and localization of Rod complexes based on local cell-envelope curvature. Using single-particle tracking of the transpeptidase and Rod-complex component PBP2, we found that PBP2 binds to a substrate different from MreB. Depletion and localization experiments of other putative Rod-complex components provide evidence that none of those provide the sole rate-limiting substrate for PBP2 binding. Consistently, we found only weak correlations between MreB and envelope curvature in the cylindrical part of cells. Residual correlations do not require curvature-based Rod-complex initiation but can be attributed to persistent rotational motion. We therefore speculate that the local cell-wall architecture provides the cue for Rod-complex initiation, either through direct binding by PBP2 or through an unknown intermediate.
Objectives The aim of this study is to describe the initial experience with versacross transseptal (TS) system for transseptal puncture for the transcatheter mitral valve repair using the MitraClip device. Background Transeptal puncture is a key step in transcatheter mitral valve repair (MVR) and the use of the VersaCross system comprised of a sheath, a dilator and a radiofrequency wire has not been previously described. Methods Prospective single center study of consecutive patients undergoing transcatheter mitral valve repair with the MitraClip device were included. Targeted TS puncture was performed under transesophageal echocardiographic (TEE) guidance. Baseline demographics, procedural characteristics, and major adverse procedural events were collected. Results Twenty‐five consecutive patients underwent transseptal puncture using the VersaCross TS system. Transseptal puncture was successful in 100% of patients. The mean time for TS puncture was 3 3 ± 1.6 min with no major adverse procedural events. The mean time from insertion of the VersaCross system to insertion of the MitraClip guide catheter was 3.8 ± 3.0 minutes. Conclusion The VersaCross TS system was successful in all patients for MitraClip procedure with no adverse procedural events and may be associated with increased procedural efficiency.
Single-particle tracking microscopy is a powerful technique to investigate how proteins dynamically interact with their environment in live cells. However, the analysis of tracks is confounded by noisy molecule localization, short tracks, and rapid transitions between different motion states, notably between immobile and diffusive states. Here, we propose a probabilistic method termed ExTrack that uses the full spatio-temporal information of tracks to extract global model parameters, to calculate state probabilities at every time point, to reveal distributions of state durations, and to refine the positions of bound molecules. ExTrack works for a wide range of diffusion coefficients and transition rates, even if experimental data deviate from model assumptions. We demonstrate its capacity by applying it to slowly diffusing and rapidly transitioning bacterial envelope proteins. ExTrack greatly increases the regime of computationally analyzable noisy single-particle tracks. The ExTrack package is available in ImageJ and Python.
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