Catalytic activity of linear-, cyclic- and polypeptides having a sequence of -Asp-β-Ala-Gly-ser-β-Ala-Gly-His-β-Ala-Gly in the hydrolysis of p-nitrophenyl acetate

Nishi, Norio; Morishige, Masaya; Tsutsumi, Atsushi; Nakajima, Bun-ichiro

doi:10.1016/0141-8130(83)90077-6

Cited by 7 publications

(2 citation statements)

References 26 publications

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“…Complexes of I-Ek-FpCytc were obtained during the course of experiments in which I-Ek was incubated with excess pigeon cytochrome c peptide by collecting the fraction at 14-16 mL (Figure la,c,e). The fraction was stored at 4 °C prior to use. Before initiating an experiment, the detergent used in the column buffer (n-dodecyl /3-D-maltoside) was replaced with the sample detergent (n-octyl /3-D-glucoside) by the following procedure.…”

Section: Methodsmentioning

confidence: 99%

Antigenic peptide binding to the mouse major histocompatibility complex class II protein I-Ek. Peptide stabilization of the quarternary structure of I-Ek

Witt¹,

McConnell²

1992

J. Am. Chem. Soc.

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Major histocompatibility complex (MHC) class II MHC proteins are noncovalently associated heterodimeric (a/3) molecules that bind and display antigenic peptides to CD4+ T cells. In the present work, three reactions were investigated: (i) the binding of a fluoresceinated peptide (representing residues 89-104 of pigeon cytochrome c, FpCytc) to the purified mouse MHC class II protein I-Ek; (ii) heterodimer disassembly (ad -* a + /3); and (iii) the dissociation of FpCytc from preformed complexes (I-Ek-FpCytc). At pH 5.2, in the detergent octyl d-D-glucoside, the cleavage of heterodimeric molecules into the individual a and d subunits is inhibited by excess FpCytc but not by the nonbinding peptide representing residues 323-339 of chicken ovalbumin (Ova). The kinetic results are consistent with a reaction mechanism whereby a first-order reaction generates a reactive intermediate which then undergoes competing firstand second-order reactions. The parallel cleavage and binding reactions have the same rate when [FpCytc] ~30 mM. The results demonstrate that a class II-peptide complex is significantly less prone to cleavage than the reactive heterodimeric intermediate; thus, peptide stabilizes the quarternary structure of MHC class II molecules. mune-related cell-surface macromolecules.1'2 MHC class II molecules are found on specialized cells of the immune system such as macrophages, dendritic cells, and B-cells; these cells proteolytically degrade foreign proteins into peptides,3 which then bind to the class II molecules.4 The resultant class II-peptide complexes are displayed on the cell-surface and engage in cell-cell communication with helper T-cells (CD4+).5 Each organism possesses a limited number of different MHC class II molecules. The MHC molecules have evidently evolved to have a dual responsibility with respect to peptide binding. Each MHC molecule can bind many different peptides and retains each of these peptides in its binding site for long periods of time, of orders of hours or days. Thus, the common paradigm of the association of high specificity and high affinity (and low off-rates) is not applicable to these complexes. Unique structural and kinetic mechanisms may be required to understand these unusual complexes.MHC class II proteins are composed of noncovalently associated a (~32 kD) and 8 (~28 kD) subunits. Each subunit is a transmembrane glycoprotein with four domains. The extracellular domain of the intact heterodimer contains the polymorphic region and is thought to contain the binding site for antigens. No X-ray crystallographic data are available for any MHC class II protein.A model for the structure of class II proteins has been proposed based on the crystal structure of the homologous MHC class I molecule, HLA-A2.6 For a review of MHC class II protein structure and function see ref 7.Previous equilibrium binding and kinetic studies have uncovered two significant features relating to MHC class II-peptide interactions. Only a fraction (10-60%) of the binding sites of affinity purified molecules b...

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Section: Methodsmentioning

confidence: 99%

Antigenic peptide binding to the mouse major histocompatibility complex class II protein I-Ek. Peptide stabilization of the quarternary structure of I-Ek

Witt¹,

McConnell²

1992

J. Am. Chem. Soc.

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“…A number of studies have shown that synthetic peptides or polypeptides can exhibit esterasic [1][2][3][4] or glycosidic [5] activity. It has also been demonstrated that the hydrolysis of the ester bonds in oligoribonucleotides, acyl esters, or DNA can be catalyzed by oligopeptides [6][7][8].…”

Section: Introductionmentioning

confidence: 99%