Abdur Siddiqi - Academia.edu (original) (raw)

Papers by Abdur Siddiqi

Amer J Pathol, 2009

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Journal of protein chemistry, 1998

Synthetic nonbasic peptides based on the type I repeats of thrombospondin (TSP) and four peptides... more Synthetic nonbasic peptides based on the type I repeats of thrombospondin (TSP) and four peptides corresponding to the predicted basic clusters in lipoprotein lipase (LPL) have been analyzed for heparin binding. In the present report we examine the structural requirement for the binding of these peptides to heparin-Sepharose column. The peptide containing the sequence Phe-Ser-Trp-Ser-Asp-Trp-Trp-Ser (residues 388-395 in lipoprotein lipase, which include the consensus TSP type I sequence) showed strong binding to heparin. Both the first and second Trp residues in this sequence were essential for tight heparin binding. Substitution of either of the Trp residues by an Ala resulted in the complete loss of heparin binding. The peptides representing the four basic cluster regions of lipoprotein lipase showed variable heparin binding. Strong retention was observed for peptides representing cluster 1 (residues 261-287) and cluster 3 (residues 147-151) peptides followed by cluster 2 (residue...

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European Journal of Biochemistry, 1991

Two phospholipase A2 isozymes have been purified from leaf-nosed viper by gel permeation chromato... more Two phospholipase A2 isozymes have been purified from leaf-nosed viper by gel permeation chromatography followed by reverse-phase HPLC and cation-exchange FPLC. Both enzymes contain seven pairs of half-cystine, typical of group II phospholipase A2. Surprisingly large differences, affecting both N- and C-terminal regions, exist between the two isozymes purified from the same snake venom. Exchanges occur at no less than 27 of 121 positions (22%), suggesting the possible existence of two genes for phospholipase A2. The residue identity with the enzymes from other Viperidae species is also low, only 44-48%, indicating extensive variations of this protein structure at large. Functionally, the present isozymes do not possess the cationic regions ascribed to myotoxicity and anti-coagulant effects of the enzyme.

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European Journal of Biochemistry, 1996

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Scandinavian Journal of Immunology, 1993

MHC-I binding peptides and beta 2 microglobulin (beta 2-m) can upregulate the MHC-I heavy chain e... more MHC-I binding peptides and beta 2 microglobulin (beta 2-m) can upregulate the MHC-I heavy chain expression on certain peptide transporter mutant cells. We have further studied this with normal cells and non-mutant cell lines. No MHC-I upregulation was seen with normal, resting or activated T cells. On mouse cell lines P815 and B16, both peptides and human beta 2-m gave an additive upregulation response. With the human small cell lung carcinoma H82, an optimal HLA.A2 binding peptide (GILGFVFTL) gave an upregulation response, whereas beta 2-m alone or in combination with this peptide had no effect. However, beta 2-m potentiated the response of H82 cells to a slightly longer peptide. Using mutant RMA-S cells, it was found that both Brefeldin A (BFA) and chloroquine, but not leupeptin, inhibited MHC-I upregulation response to both peptide and beta 2-m. In contrast to chloroquine, BFA also gave a reduction of background membrane MHC-I expression, presumably due to a block in Golgi transport. Human beta 2-m, which binds to RMA-S cells, and which is known to internalize into endosomes, did not reappear on the cell surface. When Db on RMA-S cells was upregulated by human beta 2-m, the sensitivity of these cells to Db restricted CTL cells increased. Even if beta 2-m did not upregulate the overall MHC-I expression on normal cells, it may still quantitatively increase the expression of optimally presented peptides and endosomal recycling many be important in this process.

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Peptides, 1992

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Journal of Biological Chemistry, 2000

The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) mediates agonist-induced arachidonic acid relea... more The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) mediates agonist-induced arachidonic acid release and eicosanoid production. Calcium and phosphorylation on Ser-505 by mitogen-activated protein kinases (MAPKs) regulate cPLA(2). Arachidonic acid release and eicosanoid production induced by stimuli that do (A23187, zymosan) or do not (phorbol myristate acetate (PMA), okadaic acid) mobilize calcium were quantitatively suppressed in cPLA(2)-deficient mouse peritoneal macrophages. The contribution of MAPKs to cPLA(2)-mediated arachidonic acid release was investigated. Both extracellular signal-regulated kinases (ERKs) and p38 contributed to cPLA(2) phosphorylation on Ser-505. However, although ERK inhibition did not affect A23187-induced arachidonic acid release, it suppressed zymosan-, PMA-, and okadaic acid-induced arachidonic acid release under conditions where phosphorylation of cPLA(2) on Ser-505 was unaffected. This indicates an additional regulatory mechanism for the ERK pathway. A role for transcriptional regulation is suggested by data showing that cycloheximide and actinomycin D inhibited arachidonic acid release induced by zymosan, PMA and, okadaic acid but not by A23187. Our results show that MAPK pathways contribute to arachidonic acid release in macrophages through alternative mechanisms in addition to their ability to phosphorylate cPLA(2) on Ser-505 and suggest a role for new protein synthesis.

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