PubMed · 5593595
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O Hövels. 1967. [Rickets prevention].. https://pubmed.ncbi.nlm.nih.gov/5593595/
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EF-hand peptides have been shown to bind calcium and dimerize to form an intact protein domain [Shaw, G.S., Hodges, R.S. & Sykes, B.D. (1990). Science, 249, 280-283]. A synthetic 33-residue EF-hand peptide with the sequence of carp parvalbumin CD site demonstrated a seven-fold increase in the apparent calcium dissociation constant with a eight-fold decrease in peptide concentration when fit to a single-site calcium-binding model. This observation is consistent with EF-hand dimerization. This paper describes a method to determine the dimerization dissociation constant and the calcium dissociation constants for both the monomer and dimer forms of this EF-hand peptide using circular dichroism techniques. By monitoring the increase in negative molar ellipticity at 222 nm with increasing peptide concentration under calcium-saturating conditions the dimerization dissociation constant for the synthetic parvalbumin CD site was determined to be 55.68+/-10.76 microM. Using the dimerization constant, the calcium dissociation constants for both the monomer and dimer forms of this peptide were determined by monitoring the change in ellipticity of peptide solutions on addition of increasing amounts of calcium. A fit of this data to a mathematical model that takes into account dimerization results in calcium dissociation constants of 421.3+/-21.56 and 47.06+/-6.72 microM for the monomer and dimer forms, respectively.
Platelet-endothelial cell adhesion molecule-1 (PECAM-1) is a 130-kDa transmembrane glycoprotein expressed by endothelial cells, platelets, monocytes, neutrophils, and certain T cell subsets. The PECAM-1 extracellular domain has six Ig-homology domains that share sequence similarity with cellular adhesion molecules. The PECAM-1 cytoplasmic domain contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) that, when appropriately engaged, becomes phosphorylated on tyrosine residues, creating docking sites for nontransmembrane, Src homology 2 domain-bearing protein tyrosine phosphatase (SHP)-1 and SHP-2. The purpose of the present study was to determine whether PECAM-1 inhibits protein tyrosine kinase (PTK)-dependent signal transduction mediated by the immunoreceptor tyrosine-based activation motif-containing TCR. Jurkat cells, which coexpress PECAM-1 and the TCR/CD3 complex, were INDO-1AM-labeled and then incubated with anti-CD3epsilon mAbs, anti-PECAM-1 mAbs, or both, and goat anti-mouse IgG was used to cross-link surface-bound mAbs. Calcium mobilization induced by CD3 cross-linking was found to be attenuated by coligation of PECAM-1 in a dose-dependent manner. PECAM-1-mediated inhibition of TCR signaling was attributable, at least in part, to inhibition of release of calcium from intracellular stores. These data provide evidence that PECAM-1 can dampen signals transduced by ITAM-containing receptors and support inclusion of PECAM-1 within the family of ITIM-containing inhibitors of PTK-dependent signal transduction.
Tn 10/IS 10 transposition involves excision of the transposon from a donor site and subsequent joining of the excised transposon to a new target site. These steps are catalyzed by the Tn 10 -encoded transposase protein and require the presence of a suitable divalent metal ion. Like other transposase and retroviral integrase proteins, Tn 10 transposase appears to contain a single active site which includes a triad of acidic amino acid residues generally referred to as the DDE motif. In addition to its role in catalysis, the Tn 10 transposase DDE motif also functions in target capture, a step that in vitro is greatly facilitated by the presence of a suitable divalent metal ion. We show that cysteine residue substitutions at each of the DDE motif residues in Tn 10 transposase result in a change in the divalent metal ion requirements for catalysis, such that Mn2+but not Mg2+can be used. This switch in metal ion specificity provides evidence that each of the DDE motif residues functions directly in metal ion binding. We also show differential effects of DDE mutations on metal ion-assisted target capture. A number of models, including a two metal ion active site, are considered to explain these effects.