Multitarget tracking with interacting population-based MCMC-PF

In this paper we address the problem of tracking multiple targets based on raw measurements by means of Particle filtering. This strategy leads to a high computational complexity as the number of targets increases, so that an efficient implementation of the tracker is necessary. We propose a new multitarget Particle Filter (PF) that solves such challenging problem. We call our filter Interacting Population-based MCMC-PF (IP-MCMC-PF) since our approach is based on parallel usage of multiple population-based Metropolis-Hastings (M-H) samplers. Furthermore, to improve the chains mixing properties, we exploit genetic alike moves performing interaction between the Markov Chain Monte Carlo (MCMC) chains. Simulation analyses verify a dramatic reduction in terms of computational time for a given track accuracy, and an increased robustness w.r.t. conventional MCMC based PF

Efficient characterization of labeling uncertainty in closely-spaced targets tracking

In this paper we propose a novel solution to the labeled multi-target tracking problem. The method presented is specially effective in scenarios where the targets have once moved in close proximity. When this is the case, disregarding the labeling uncertainty present in a solution (after the targets split) may lead to a wrong decision by the end user. We take a closer look at the main cause of the labeling problem. By modeling the possible crosses between the targets, we define some relevant labeled point estimates. We extend the concept of crossing objects, which is obvious in one dimension, to scenarios where the objects move in multiple dimensions. Moreover, we provide a measure of uncertainty associated to the proposed solution to tackle the labeling problem. We develop a novel, scalable and modular framework in line with it. The proposed method is applied and analyzed on the basis of one-dimensional objects and two-dimensional objects simulation experiments

The low-affinity ATP binding site of the Escherichia coli SecA dimer is localized at the subunit interface

The homodimeric SecA protein is the ATP-dependent force generator in the Escherichia coli precursor protein translocation cascade. SecA contains two essential nucleotide binding sites (NBSs), i.e., NBS1 and NBS2 that bind ATP with high and low affinity, respectively. The photoactivatable bifunctional cross-linking agent 3'-arylazido-8-azidoadenosine 5'-triphosphate (diN3ATP) was used to investigate the spatial arrangement of the nucleotide binding sites of SecA. DiN3ATP is an authentic ATP analogue as it supports SecA-dependent precursor protein translocation and translocation ATPase. UV-induced photo-cross-linking of the diN3ATP-bound SecA results in the formation of stable dimeric species of SecA. D209N SecA, a mutant unable to bind nucleotides at NBS1, was also photo-cross-linked by diN3ATP, whereas no cross-linking occurred with the NBS2 mutant R509K SecA. We concluded that the low-affinity NBS2, which is located in the carboxyl-terminal half of SecA, is the site of cross-linking and that NBS2 binds nucleotides at or near the subunit interface of the SecA dimer.

Characterization of the arcD Arginine:Ornithine Exchanger of Pseudomonas aeruginosa. Localization in the Cytoplasmic Membrane and a Topological Model

The arcDABC operon of Pseudomonas aeruginosa encodes the enzymes of the arginine deiminase pathway and is induced by oxygen limitation. The arcD gene specifies a 53-kDa protein with arginine: ornithine exchange activity. The ArcD protein of P. aeruginosa, like the LysI lysine transporter of Corynebacterium glutamicum, has 13 hydrophobic regions which could span the cytoplasmic membrane. Fusion of a Caa (colicin A) epitope to the N-terminal part of ArcD permitted the localization, by immunoblotting, of the hybrid protein in the inner membrane of P. aeruginosa. Fusion of PhoA (alkaline phosphatase) to the very C terminus of ArcD produced another hybrid protein, which exhibited PhoA activity. Both ArcD hybrid proteins retained arginine transport activity and served to support a topological model which proposes that the N terminus is oriented toward the cytoplasm and the C terminus faces the periplasm. Further ArcD-PhoA fusions were consistent with this model. When the Caa epitope was fused to a C-terminal ArcD fragment consisting of only 5 hydrophobic domains, the resulting hybrid protein could be recovered intact from the inner membrane, suggesting that the C-terminal part of ArcD contains sufficient information for insertion into the membrane. This study illustrates the utility of the Caa epitope to tag membrane proteins