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A Kharrat

Publications and source records attributed to A Kharrat.

10 recordsLinked to original sources
PubMed1998

Conformational stability studies of the pleckstrin DEP domain: definition of the domain boundaries.

Pleckstrin is the major substrate of protein kinase C in platelets. It contains at its N- and C-termini two pleckstrin homology (PH) domains which have been proposed to mediate protein-protein and protein-lipid interactions. A new module, called DEP, has recently been identified by sequence analysis in the central region of pleckstrin. In order to study this module, several recombinant polypeptides corresponding to the DEP module and N- and C-termini extended forms have been expressed. Using circular dichroism (CD) and nuclear magnetic resonance (NMR) techniques, the domain boundaries have been determined that yield a soluble and folded pleckstrin DEP domain. This comprises 93 amino acids with an alpha/beta fold in agreement with secondary structure predictions. Stability studies indicate that the regions surrounding the DEP domain do not contribute to its stability suggesting that the phosphorylation sites at S113, T114 and S117 are in an unstructured region. Identification of the regions of pleckstrin that are folded shall facilitate determination of its structure and function.

Amino Acid Sequence↗
PubMed1995

Structure of the dsRNA binding domain of E. coli RNase III.

The double-stranded RNA binding domain (dsRBD) is a approximately 70 residue motif found in a variety of modular proteins exhibiting diverse functions, yet always in association with dsRNA. We report here the structure of the dsRBD from RNase III, an enzyme present in most, perhaps all, living cells. It is involved in processing transcripts, such as rRNA precursors, by cleavage at short hairpin sequences. The RNase III protein consists of two modules, a approximately 150 residue N-terminal catalytic domain and a approximately 70 residue C-terminal recognition module, homologous with other dsRBDs. The structure of the dsRBD expressed in Escherichia coli has been investigated by homonuclear NMR techniques and solved with the aid of a novel calculation strategy. It was found to have an alpha-beta-beta-beta-alpha topology in which a three-stranded anti-parallel beta-sheet packs on one side against the two helices. Examination of 44 aligned dsRBD sequences reveals several conserved, positively charged residues. These residues map to the N-terminus of the second helix and a nearby loop, leading to a model for the possible contacts between the domain and dsRNA.

Amino Acid Sequence↗
PubMed1992

Concerted activities of the RNA recognition and the glycine-rich C-terminal domains of nucleolin are required for efficient complex formation with pre-ribosomal RNA.

Nucleolin is an abundant nucleolar protein which is involved in the early stages of ribosome assembly. The central 40-kDa domain of nucleolin comprises four RNA recognition motifs (RRM) which are presumed to be involved in specific interactions with pre-rRNA. In order to examine in detail the role of this central domain and the contribution of the N-terminal and C-terminal domains of nucleolin to RNA binding, we have used an Escherichia coli expression system to synthezise polypeptides corresponding to various combinations of the three domains and their subdomains. By means of an in-vitro binding assay and a synthetic RNA corresponding to a specific recognition site in pre-rRNA we have been able to demonstrate conclusively that the central 40-kDa domain is indeed responsible for the specificity of RNA recognition and that the N-terminal domain can be removed without affecting RNA binding. Most interestingly, it appears that the C-terminal 10-kDa domain, which is rich in glycine and arginine residues, is essential for efficient binding of nucleolin to RNA, but does not itself contribute to the specificity of the interaction. Circular dichroic spectroscopic probing of the RNA component shows that the C-terminal domain significantly modifies the RNA-binding properties of the central RRM core. Finally, infrared spectroscopic studies reveal that the central 40-kDa domain is structured in alpha helices and beta sheets and that the interaction with the specific pre-rRNA site induces subtle changes in the beta sheet conformation.

Binding Sites↗
PubMed1991

Synergistic effect of histone H1 and nucleolin on chromatin condensation in mitosis: role of a phosphorylated heteromer.

Repeated motifs, rich in basic residues, are characteristic of both the N-terminal domain of the nucleolus-specific protein, nucleolin, and the second half of the C-terminal domain of histone H1. These repeats are also the target for phosphorylation by the mitosis-specific p34cdc2 kinase. We have previously shown that synthetic peptides [(KTPKKAKKP)2 for histone H1 and (ATPAKKAA)2 for nucleolin] corresponding to these two repeated motifs are able to act in synergy to induce DNA hypercondensation (Erard et al., 1990). In order to determine the molecular basis of this synergistic interaction, we have studied the condensation of the homopolymer poly(dA).poly(dT) in the presence of the two synthetic peptides. Circular dichroism has been used to monitor the psi (+)-type condensation and has revealed that phosphorylation enhances the synergistic effect of the two peptides. Analysis of different combinations of the two peptides suggests that there is a direct interaction between them which is stabilized by phosphorylation. Furthermore, there is a striking correlation between the degree of homopolymer condensation and the stability of the heteromeric complex. Phosphorylation takes place on the threonine residues on the repeat motifs within a region which is likely to adopt a beta-turn structure. Circular dichroism and infrared spectroscopy provide evidence that phosphorylation stabilizes the beta-turn structure of both peptides, and computer modeling shows that this may be due to steric hindrance imposed by the phosphate group. We suggest that phosphorylated nucleolin and histone H1 interact through their homologous domain structured in beta-spirals in order to condense certain forms of DNA during mitosis.

Amino Acid Sequence↗
PubMed1983

[Algodystrophy and metabolic abnormalities].

The French Society of Rheumatology national study of reflex dystrophy revealed a serum glucose greater than 1.20 g/l in 9.09 p. cent of cases, a serum uric acid greater than 70 mg/l in 25 p. cent of men and greater than 60 mg/l in 14 p. cent of women. Serum cholesterol was normal in males, but higher than the mean + 2 sigma in 23 p. cent of females. Serum triglycerides were higher than m + 2 sigma in 55 p. cent of men and 56 p. cent of women. From a group of 80 patients, 54 (67.5 p. cent) had at least one of the three metabolic abnormalities and 49 (61.25 p. cent) were hypertriglyceridaemic. This hypertriglyceridaemia is the most frequent abnormality found. When hyperglycaemia or hyperuricaemia are present it is almost always in association with hypertriglyceridaemia. Hypertriglyceridaemia is more common in algoneurodystrophy of the lower limbs (54/78, 69 p. cent) than in algoneurodystrophy of the upper limbs (5/22, 22.7 p. cent). Algoneurodystrophy is more often primary, when it occurs in the lower limbs and post-traumatic when it occurs in the upper limbs. A prospective study comparing several parameters of lipid metabolism in 24 patients with algoneurodystrophy and 15 matched controls showed a significant drop in the HDL Chol/HDL P1 ratio and in the DHL - HDL Chol/TG ratio in patients with algoneurodystrophy. Serum insulin was comparable in the 2 groups. Lecithin cholesterol acyl transferase (LCAT), SGOT, SGPT and GGT were normal. The essential role of hypertriglyceridaemia in the genesis of the characteristic bony lesions of algoneurodystrophy is discussed.

Adolescent↗
PubMed1982

[Algodystrophy and metabolic anomalies].

The French Society of Rheumatology national study of reflex dystrophy revealed a serum glucose greater than 1.20 g/l in 9.09 p. cent of case, a serum uric acid greater than 70 mg/l in 25 p. cent of men and greater than 60 mg/l in 14 p. cent of women. Serum cholesterol was normal in male cases, but higher than the mean + 2 sigma in 23 p. cent of female cases. Serum triglycerides was higher than m + 2 sigma in 55 p. cent of men and 56 p. cent of women. From a group of 80 patients, 54 (67.5 p. cent) had at least one of the three metabolic abnormalities and 49 (61.25 p. cent) were hypertriglyceridaemic. This hypertriglyceridaemia is the most frequent abnormality found. When hyperglycaemia or hyperuricaemia are present it is almost always in association with hypertriglyceridaemia. Hypertriglyceridaemia is more common in algoneurodystrophy of the lower limbs (54/78, 69 p. cent) than in algoneurodystrophy of the upper limbs (5/22, 22.7 p. cent). Algoneurodystrophy is more often primary, when it occurs in the lower limbs and post-traumatic when it occurs in the upper limbs. A prospective study comparing several parameters of lipid metabolism between 24 patients with algoneurodystrophy and 15 matched controls showed a significant drop in the HDL Chol/HDL P1 ratio and in the DHL--HDL Chol/TG ratio in patients with algoneurodystrophy. Serum insulin was comparable in the 2 groups. Lecithin cholesterol acyl transferase (LCAT), SGOT, SGPT and GGT were normal. The essential role of hypertriglyceridaemia in the genesis of the characteristic bony lesions of algoneurodystrophy is discussed.

Adult↗
PubMedDate not supplied

[Incidence of amplification of the C-erb B2/Her-2/neu gene in human breast cancer].

Activation of cellular proto-oncogenes can be detected in several human cancers. In the current study, alterations of C-erb B2 gene in primary human breast cancers were investigated. It was found to be amplified from 2 to 30 fold in 25% of the tumors. Correlations of gene amplification with several disease parameters was evaluated.

Adult↗
PubMedDate not supplied

[Characterization of nucleolar organizers in carcinomatous mammmary lesions].

An argyrophil stain for nucleolar organizer regions (NORs) has been applied to paraffin sections of 24 malignant and 3 benign breast tumors. It was found that the total number of Ag-NORs in malignant breast lesions (3.66) significantly exceeded those in benign lesions (1.65). Relationship between this index and some clinical parameters was studied. A positive correlation between NORs and histological grading and prognostic was found.

Adult↗
PubMedDate not supplied

Type IV hyperlipoproteinemia in patients with algodystrophy.

The present work studies lipid metabolism in patients with algodystrophy (AD). A correct positive correlation (r = 0.75) between the triglyceride levels and low density lipoprotein (LDL)/very low density lipoprotein (VLDL) ratio and the VLDL increase observed by gel disk electrophoresis confirm that a type IV hyperlipoproteinemia is associated with AD. In contrast, the degree of high density lipoprotein (HDL) saturation in cholesterol (HDL-cholesterol/HDL-phospholipids) and the classical atherogenous index (cholesterol/HDL-cholesterol) were not modified. The decrease of plasma post-heparin lipolytic activities (PHLA) was not significant but further studies should be performed to correlate PHLA with a reduced activity of the adipose tissue lipoprotein lipase.

Cholesterol↗