Biomedical subjects

Fei Long

Publications and source records attributed to Fei Long.

11 recordsLinked to original sources

PubMed2006

Genetic mapping of allometric scaling laws.

Many biological processes, from cellular metabolism to population dynamics, are characterized by particular allometric scaling relationships between rate and size (power laws). A statistical model for mapping specific quantitative trait loci (QTLs) that are responsible for allometric scaling laws has been developed. We present an improved model for allometric mapping of QTLs based on a more general allometry equation. This improved model includes two steps: (1) use model II regression analysis to estimate the parameters underlying universal allometric scaling laws, and (2) substitute the estimated allometric parameters in the mixture-based mapping model to obtain the estimation of QTL position and effects. This model has been validated by a real example for a mouse F2 progeny, in which two QTLs were detected on different chromosomes that determine the allometric relationship between growth rate and body weight.

Algorithms↗

PubMed2005

PKA-mediated protein phosphorylation protects ezrin from calpain I cleavage.

Ezrin is localized to the apical membrane of parietal cells and couples the cAMP-dependent protein kinase (PKA) activation cascade to the regulated HCl secretion in gastric parietal cells. Our recent studies demonstrate the functional relevance of PKA-mediated phosphorylation of ezrin in parietal cell secretion [R. Zhou, X. Cao, C. Watson, Y. Miao, Z. Guo, J.G. Forte, X. Yao, Characterization of protein kinase A-mediated phosphorylation of ezrin in gastric parietal cell activation, J. Biol. Chem. 278 (2003) 35651]. Here we show that activation of PKA protects ezrin from calpain I-mediated proteolysis without alteration of calpain I activation and fodrin breakdown. To determine whether phosphorylation of Ser66 by PKA affects the insensitivity to the calpain I-mediated cleavage, recombinant proteins of ezrin, both wild type and S66A/D mutants, were incubated with the purified calpain I. Indeed, phosphorylation-like S66D mutant ezrin is resistant to calpain I-mediated proteolysis while wild type and S66A mutant were sensitive. In fact, expression of phosphorylation-like S66D, but not S66A, mutant in parietal cells confers its resistance to calpain I-mediated proteolysis. Taken together, these results indicate that phosphorylation of ezrin by PKA modulates its sensitivity to calpain I cleavage.

Animals↗

PubMed2005

X-ray reflectivity studies of cPLA2{alpha}-C2 domains adsorbed onto Langmuir monolayers of SOPC.

X-ray reflectivity is used to study the interaction of C2 domains of cytosolic phospholipase A(2) (cPLA(2)alpha-C2) with a Langmuir monolayer of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) supported on a buffered aqueous solution containing Ca(2+). The reflectivity is analyzed in terms of the known crystallographic structure of cPLA(2)alpha-C2 domains and a slab model representing the lipid layer to yield an electron density profile of the lipid layer and bound C2 domains. This new method of analysis determines the angular orientation and penetration depth of the cPLA(2)alpha-C2 domains bound to the SOPC monolayer, information not available from the standard slab model analysis of x-ray reflectivity. The best-fit orientation places the protein-bound Ca(2+) ions within 1 A of the lipid phosphate group (with an accuracy of +/-3 A). Hydrophobic residues of the calcium-binding loops CBL1 and CBL3 penetrate deepest into the lipid layer, with a 2 A penetration into the tailgroup region. X-ray measurements with and without the C2 domain indicate that there is a loss of electrons in the headgroup region of the lipid monolayer upon binding of the domains. We suggest that this is due to a loss of water molecules bound to the headgroup. Control experiments with a non-calcium buffer and with domain mutants confirm that the cPLA(2)alpha-C2 binding to the SOPC monolayer is Ca(2+)-dependent and that the hydrophobic residues in the calcium-binding loops are critical for membrane binding. These results indicate that an entropic component (due to water loss) as well as electrostatic and hydrophobic interactions contributes to the binding mechanism.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2005

PALS1 specifies the localization of ezrin to the apical membrane of gastric parietal cells.

The ERM (ezrin/radixin/moesin) proteins provide a regulated linkage between membrane proteins and the cortical cytoskeleton and also participate in signal transduction pathways. Ezrin is localized to the apical membrane of parietal cells and couples the protein kinase A activation cascade to regulated HCl secretion in gastric parietal cells. Here, we show that the integrity of ezrin is essential for parietal cell activation and provide the first evidence that ezrin interacts with PALS1, an evolutionarily conserved PDZ and SH3 domain-containing protein. Our biochemical study verifies that ezrin binds to PALS1 via its N terminus and is co-localized with PALS1 to the apical membrane of gastric parietal cells. Furthermore, our study shows that PALS1 is essential for the apical localization of ezrin, as either suppression of PALS1 protein accumulation or deletion of the PALS1-binding domain of ezrin eliminated the apical localization of ezrin. Finally, our study demonstrates the essential role of ezrin-PALS1 interaction in the apical membrane remodeling associated with parietal cell secretion. Taken together, these results define a novel molecular mechanism linking ezrin to the conserved apical polarity complexes and their roles in polarized epithelial secretion of gastric parietal cells.

Animals↗

PubMed2005

[Non-genomic actions of steroids: mechanism and significance].

It has been demonstrated that all steroids can exert their actions by rapid non-genomic effects. Different steroids have different non-genomic mechanism. And there always occurs some new mechanism after some time. Now we review the non-genomic mechanism and significance of steroids.

Animals↗

PubMed2004

Rapid nongenomic inhibitory effects of glucocorticoids on phagocytosis and superoxide anion production by macrophages.

Traditionally, steroid hormone effects have been described as a result of the modulation of nuclear transcription, thus triggering genomic events that are responsible for physiological effects. Despite early observations of rapid steroid effects that were incompatible with this theory, nongenomic steroid effects have been widely recognized only recently. However, the nongenomic effect of glucocorticoid (GC) on anti-inflammation and immunosuppression has not been reported. Macrophages play important roles in inflammation and the immune response. The present experiment selected macrophages as experimental cells to explore the nongenomic effects and possible mechanisms of GCs on phagocytosis and superoxide anion production. Phagocytosis by macrophages was detected by the neutral red uptake assay. The superoxide anions were measured by cytochrome C reduction assay. It was found that both 10(-4) and 10(-5) mol/L corticosterone (CORT) rapidly inhibited uptake of neutral red by macrophages in less than 30 min, and the inhibition by the former was stronger than that of the latter. CORT (10(-4) to 10(-10) mol/L) rapidly inhibited superoxide anion production by macrophages in less than 30 min. The above-mentioned effects were insensitive to the GC-receptor antagonist mifepristone (RU486) and the translation inhibitor actidione. CORT coupled to bovine serum albumin (BSA-CORT) was able to mimic the rapid inhibitory effects of CORT. The results indicated that CORT could rapidly inhibit phagocytosis and superoxide anion production by mouse peritoneal macrophages in vitro in less than 30 min by a rapid, nongenomic mechanism, which contributes to the anti-inflammatory and immunosuppressive actions of GCs. These data shed a new light on the clinical application of GCs.

Animals↗

PubMed2004

REFMAC5 dictionary: organization of prior chemical knowledge and guidelines for its use.

One of the most important aspects of macromolecular structure refinement is the use of prior chemical knowledge. Bond lengths, bond angles and other chemical properties are used in restrained refinement as subsidiary conditions. This contribution describes the organization and some aspects of the use of the flexible and human/machine-readable dictionary of prior chemical knowledge used by the maximum-likelihood macromolecular-refinement program REFMAC5. The dictionary stores information about monomers which represent the constitutive building blocks of biological macromolecules (amino acids, nucleic acids and saccharides) and about numerous organic/inorganic compounds commonly found in macromolecular crystallography. It also describes the modifications the building blocks undergo as a result of chemical reactions and the links required for polymer formation. More than 2000 monomer entries, 100 modification entries and 200 link entries are currently available. Algorithms and tools for updating and adding new entries to the dictionary have also been developed and are presented here. In many cases, the REFMAC5 dictionary allows entirely automatic generation of restraints within REFMAC5 refinement runs.

Chemical Phenomena↗

PubMed2003

Contrasting membrane interaction mechanisms of AP180 N-terminal homology (ANTH) and epsin N-terminal homology (ENTH) domains.

Epsin and AP180/CALM are endocytotic accessory proteins that have been implicated in the formation of clathrin-coated pits. Both proteins have phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2)-binding domains in their N termini, but these domains are structurally and functionally different. To understand the basis of their distinct properties, we measured the PtdIns(4,5)P2-dependent membrane binding of the epsin N-terminal homology (ENTH) domain and the AP180 N-terminal homology (ANTH) domain by means of surface plasmon resonance and monolayer penetration techniques and also calculated the effect of PtdIns(4,5)P2 on the electrostatic potential of these domains. PtdIns(4,5)P2 enhances the electrostatic membrane association of both domains; however, PtdIns(4,5)P2 binding exerts distinct effects on their membrane dissociation. Specifically, PtdIns(4,5)P2 induces the membrane penetration of the N-terminal alpha-helix of the ENTH domain, which slows the membrane dissociation of the domain and triggers the membrane deformation. These results provide the biophysical explanation for the membrane bending activity of epsin and its ENTH domain.

Adaptor Proteins, Vesicular Transport↗

PubMed2003

[Application of complexity sequence in sleep staging based on sleep EEG data].

In this paper an approach of time-window complexity sequence is applied to sleep EEG analysis. This approach can reduce the loss of state information due to the nonstationarity of EEG signal and the unevenness of state space, and can overcome certain limitations of the complexity itself to some extent. It will help to extract the state features of EEG in different sleep stages. In addition, we preprocess EEG by adopting ICA and wavelet transform (WT). The results show that some physiological artifact in EEG can be eliminated effectively by these methods, and the sleep staging based on sleep EEG data will be more exact.

Algorithms↗

PubMed2003

[Eliminating artifacts of EEG data based on independent component analysis].

As a new array processing technique, independent component analysis(ICA) is an effective means to resolve the blind source separation(BSS) problem. Based on the brief introductions of ICA theory and algorithm, we apply ICA to the removal of ocular artifacts from EEG recordings. The EEG data collected from the human scalp is actually the mixtures of some independent components. It is coincident with the basic assumptions of ICA. Compared with the traditional methods of artifacts elimination, ICA, a kind of spatial filter, is not restricted by the case of spectrum overlapping, and it has a good reservation of useful detail signals. In addition, the inverse weight matrix of ICA can be used to reflect the topographic structure of different independent sources of EEG.

Algorithms↗

PubMed2002

Phosphatidylinositol 3-phosphate induces the membrane penetration of the FYVE domains of Vps27p and Hrs.

The FYVE domain mediates the recruitment of proteins involved in membrane trafficking and cell signaling to phosphatidylinositol 3-phosphate (PtdIns(3)P)-containing membranes. To elucidate the mechanism by which the FYVE domain interacts with PtdIns(3)P-containing membranes, we measured the membrane binding of the FYVE domains of yeast Vps27p and Drosophila hepatocyte growth factor-regulated tyrosine kinase substrate and their mutants by surface plasmon resonance and monolayer penetration analyses. These measurements as well as electrostatic potential calculation show that PtdIns(3)P specifically induces the membrane penetration of the FYVE domains and increases their membrane residence time by decreasing the positive charge surrounding the hydrophobic tip of the domain and causing local conformational changes. Mutations of hydrophobic residues located close to the PtdIns(3)P-binding pocket or an Arg residue directly involved in PtdIns(3)P binding abrogated the penetration of the FYVE domains into the monolayer, the packing density of which is comparable with that of biological membranes and large unilamellar vesicles. Based on these results, we propose a mechanism of the membrane binding of the FYVE domain in which the domain first binds to the PtdIns(3)P-containing membrane by specific PtdIns(3)P binding and nonspecific electrostatic interactions, which is then followed by the PtdIns(3)P-induced partial membrane penetration of the domain.

Animals↗