Interactions of histatin-3 and histatin-5 with actin

Background

Histatins are histidine rich polypeptides produced in the parotid and submandibular gland and secreted into the saliva. Histatin-3 and ?5 are the most important polycationic histatins. They possess antimicrobial activity against fungi such as Candida albicans. Histatin-5 has a higher antifungal activity than histatin-3 while histatin-3 is mostly involved in wound healing in the oral cavity. We found that these histatins, like other polycationic peptides and proteins, such as LL-37, lysozyme and histones, interact with extracellular actin.

Results

Histatin-3 and ?5 polymerize globular actin (G-actin) to filamentous actin (F-actin) and bundle F-actin filaments. Both actin polymerization and bundling by histatins is pH sensitive due to the high histidine content of histatins. In spite of the equal number of net positive charges and histidine residues in histatin-3 and ?5, less histatin-3 is needed than histatin-5 for polymerization and bundling of actin. The efficiency of actin polymerization and bundling by histatins greatly increases with decreasing pH. Histatin-3 and ?5 induced actin bundles are dissociated by 100 and 50 mM NaCl, respectively. The relatively low NaCl concentration required to dissociate histatin-induced bundles implies that the actin-histatin filaments bind to each other mainly by electrostatic forces. The binding of histatin-3 to F-actin is stronger than that of histatin-5 showing that hydrophobic forces have also some role in histatin-3- actin interaction. Histatins affect the fluorescence of probes attached to the D-loop of G-actin indicating histatin induced changes in actin structure. Transglutaminase cross-links histatins to actin. Competition and limited proteolysis experiments indicate that the main histatin cross-linking site on actin is glutamine-49 on the D-loop of actin.

Conclusions

Both histatin-3 and ?5 interacts with actin, however, histatin 3 binds stronger to actin and affects actin structure at lower concentration than histatin-5 due to the extra 8 amino acid sequence at the C-terminus of histatin-3. Extracellular actin might regulate histatin activity in the oral cavity, which should be the subject of further investigation.

     

Capillary electrophoresis for the analysis of paralytic shellfish poisoning toxins in shellfish: Comparison of detection methods

Paralytic shellfish toxins (PSTs) are produced by marine and freshwater microalgae and accumulate in shellfish including mussels, oysters, and scallops, causing possible fatalities when inadvertently consumed. Monitoring of PST content of shellfish is therefore important for food safety, with currently approved methods based on HPLC, using pre‐ or postcolumn oxidation for fluorescence detection (HPLC‐FLD). CE is an attractive alternative for screening and detection of PSTs as it is compatible with miniaturization and could be implemented in portable instrumentation for on‐site monitoring. In this study, CE methods were developed for C⁴D, FLD, UV absorption detection, and MS—making this first report of C⁴D and FLD for PSTs detection. Because most oxidized toxins are neutral, MEKC was used in combination with FLD. The developed CZE‐UV and CZE‐C⁴D methods provide better resolution, selectivity, and separation efficiency compared to CZE‐MS and MEKC‐FLD. The sensitivity of the CZE‐C⁴D and MEKC‐FLD methods was superior to UV and MS, with LOD values ranging from 140 to 715 ng/mL for CZE‐C⁴D and 60.9 to 104 ng/mL for MEKC‐FLD. With the regulatory limit for shellfish samples of 800 ng/mL, the CZE‐C⁴D and MEKC‐FLD methods were evaluated for the screening and detection of PSTs in shellfish samples. While the CZE‐C⁴D method suffered from significant interferences from the shellfish matrix, MEKC‐FLD was successfully used for PST screening of a periodate‐oxidized mussel sample, with results confirmed by HPLC‐FLD. This confirms the potential of MEKC‐FLD for screening of PSTs in shellfish samples.     

Photoionization and Pyrolysis of a 1,4‐Azaborinine: Retro‐Hydroboration in the Cation and Identification of Novel Organoboron Ring Systems

The photoionization and dissociative photoionization of 1,4‐di‐tert‐butyl‐1,4‐azaborinine by means of synchrotron radiation and threshold photoelectron photoion coincidence spectroscopy is reported. The ionization energy of the compound was determined to be 7.89 eV. Several low‐lying electronically excited states in the cation were identified. The various pathways for dissociative photoionization were modeled by statistical theory, and appearance energies AE_0K were obtained. The loss of isobutene in a retro‐hydroboration reaction is the dominant pathway, which proceeds with a reverse barrier. Pyrolysis of the parent compound in a chemical reactor leads to the generation of several yet unobserved boron compounds. The ionization energies of the C₄H₆BN isomers 1,2‐ and 1,4‐dihydro‐1,4‐azaborinine and the C₃H₆BN isomer 1,2‐dihydro‐1,3‐azaborole were determined from threshold photoelectron spectra.     

Travel Time Tomography

We survey some results on travel time tomography. The question is whether we can determine the anisotropic index of refraction of a medium by measuring the travel times of waves going through the medium. This can be recast as geometry problems, the boundary rigidity problem and the lens rigidity problem. The boundary rigidity problem is whether we can determine a Riemannian metric of a compact Riemannian manifold with boundary by measuring the distance function between boundary points. The lens rigidity problem problem is to determine a Riemannian metric of a Riemannian manifold with boundary by measuring for every point and direction of entrance of a geodesic the point of exit and direction of exit and its length. The linearization of these two problems is tensor tomography. The question is whether one can determine a symmetric two-tensor from its integrals along geodesics. We emphasize recent results on boundary and lens rigidity and in tensor tomography in the partial data case, with further applications.     

A Sharp Version of Mahler's Inequality for Products of Polynomials

In this note we give some sharp estimates for norms of polynomialsvia the products of norms of their linear terms. Different convexnorms on the unit disc are considered. 1991 Mathematics SubjectClassification 30C10, 11C08.     

Structural reconfiguration and informal coordination in administrative organizations

This paper considers the problem of determining the optimal design of public organizations in terms of maximizing their reliability against institutional failures. To capture both the individual and the system-level aspects of organizational decisionmaking, first we present an analytical model that characterizes the optimal decision behavior of a single decision maker (unit, agent, in general: DM) in the context of a binary decision task. In this sense, reliability of a DM against the two possible error types: implementation of the wrong policy (error of comission, Type I error) and failure to act when it is necessary (error of omission, Type II error) are interpreted as the result of a particular decision strategy. Individual expertise is represented in the form of a Relative Operating Characteristic (ROC) curve that, in turn, depicts the necessary trade-off between the two errors when selecting an appropriate decision strategy. Component decisions are then combined along the lines of organizational structure which is described using a graph formalism. We show that the task of finding the best organizational design involves a joint optimization over structure and strategy, and implement the normative model in the context of a detailed example. Our numerical results suggest that when DMs coordinate their decision rules, there is little difference in the performance of various organizational structures.This work was supported by the Office of Naval Research under ONR contract #N0014-93-I-0793.