Kir2.1 (also known as IRK1) plays key roles in the regulation of resting membrane potential and cell excitability. To achieve its physiological roles, Kir2.1 performs a series of conformational transitions, named as gating. However, the structural basis of gating is still obscure. Here, we combined site-directed mutagenesis, two-electrode voltage clamp with molecular dynamics simulations and determined that H221 regulates the gating process of Kir2.1 by involving a weak interaction network. Our data show that the H221R mutant accelerates the rundown kinetics and decelerates the reactivation kinetics of Kir2.1. Compared with the WT channel, the H221R mutation strengthens the interaction between the CD- and G-loops (E303-R221) which stabilizes the close state of the G-loop gate and weakens the interactions between C-linker and CD-loop (R221-R189) and the adjacent G-loops (E303-R312) which in turn destabilizes the open state of G-loop gate. Our data indicate that the three pairs of interactions (E303-H221, H221-R189 and E303-R312) precisely regulate the G-loop gate by controlling the conformation of the G-loop.
Calcium ions bind at the gating ring which triggers the gating of BK channels. However, the allosteric mechanism by which Ca2+ regulates the gating of BK channels remains obscure. Here, we applied Molecular Dynamics (MD) and Targeted MD to the integrated gating ring of BK channels, and achieved the transition from the closed state to a half-open state. Our date show that the distances of the diagonal subunits increase from 41.0 Å at closed state to 45.7Å or 46.4 Å at a half-open state. It is the rotatory motion and flower-opening like motion of the gating rings which are thought to pull the bundle crossing gate to open ultimately. Compared with the ‘Ca2+ bowl’ at RCK2, the RCK1 Ca2+ sites make more contribution to opening the channel. The allosteric motions of the gating ring are regulated by three group of interactions. The first weakened group is thought to stabilize the close state; the second strengthened group is thought to stabilize the open state; the third group thought to lead AC region forming the CTD pore to coordinated motion, which exquisitely regulates the conformational changes during the opening of BK channels by Ca2+.
Abstract. In this paper, a monocular vision measurement system based on cooperative targets detection is proposed, which can capture the three-dimensional information of objects by recognizing the checkerboard target and calculating of the feature points. The aircraft pose measurement is an important problem for aircraft's monitoring and control. Monocular vision system has a good performance in the range of meter. This paper proposes an algorithm based on coplanar rectangular feature to determine the unique solution of distance and angle. A continuous frame detection method is presented to solve the problem of corners' transition caused by symmetry of the targets. Besides, a displacement table test system based on three-dimensional precision and measurement system human-computer interaction software has been built. Experiment result shows that it has a precision of 2mm in the range of 300mm to 1000mm, which can meet the requirement of the position measurement in the aircraft cabin. IntroductionThe aircraft pose measurement system is an important subject of aircraft monitoring and control. Rich information can be obtained by visual measurement methods, which has a good performance in short distance. Targets detection in visual measurement can be divided into cooperative targets and non-cooperative targets. When measuring based on a cooperative target, a target made with a specific size and shape is used, together with a single camera to require pictures of it. The key problem of monocular vision measurement is target detection and pose solution [5,7,8]. Target detection is to detect the feature points for the later calculation. In the aspect of target detection, this paper uses the checkerboard as the target to detect the four corners of the boundary, which transforms the problem into similar P4P problem with four points as the characteristic point [2]. In terms of pose solution, a four-point fixed method based on spatial fixation is adopted.In order to verify the measurement range and precision of the whole measurement system, a stepper motor is used to test the distance and angle of X, Y and Z in three directions. The reliability and measurement of the algorithm accuracy is verified as well at the same time. The human-computer interaction interface based on MFC (Microsoft Foundation Classes) is developed, and the location information can be observed in real time and the intuitive real-time dynamic curve is displayed. Experiment shows that the chessboard target has more features and is easy to extract the feature reliability, and the extracted feature pixel is sub-pixel level, which can meet the requirement of high precision calculation within 300mm ~ 1000mm.
A novel method called global and local transformation consistency constraints, which combines the scale, orientation and spatial layout information of 'scale invariant feature transform' (SIFT) features, is proposed for discarding mismatches from given putative point correspondences. Experiments show that the proposed method can efficiently extract high-precision matches from low-precision putative SIFT matches for wide baseline image pairs, and outperforms or performs close to state-of-the-art approaches.Introduction: Local features are powerful tools for finding correspondences between wide baseline views of the same scenes. Some feature-based algorithms first establish putative correspondences, and then estimate the best global geometry relationship (such as homography) interpreting them. However, many well-known robust estimators (such as RANSAC [1]) perform poorly when the ratio of inliers is lower than 50% [2], while discarding mismatches before estimating this relationship yields important improvements, especially in the case where incorrect matches strongly outnumber the correct ones. Previous works (see e.g. [3,4]) for discarding mismatches mainly employ the geometrical and topological relationship among putative matches, but ignore the scale and orientation information of the potential feature pairs, which can express a similarity transformation.This Letter focuses on rejecting mismatches via evaluating the quality of each potential correspondence, which is measured by both global and local transformation consistency. To address the mismatches discarding problem, we divide the algorithm into two steps. First, using global constraint, we will be retaining a part of the matches of which the scale log-ratio and orientation difference are approximate to global scaling and rotation factor, respectively. Then, using local constraint, we will reject more incorrect matches from the first step, with a stricter constraint by requiring that neighbouring feature pairs have the similar transformation. Experiments show that the approach presented in this Letter improves the currently achieved wide baseline matching precision, with 10% fewer errors on most of the six well-known wide baseline image pairs, which were offered by Tuytellaars and Van Gool [5].
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