peptide

(noun)

A class of organic compounds consisting of various numbers of amino acids, in which the amine of one is reacted with the carboxylic acid of the next to form an amide bond.

Related Terms

Examples of peptide in the following topics:

  • Nonribosomal Peptide Antibiotics

    • Nonribosomal peptides (NRP) are a class of peptide secondary metabolites which can function as antibiotics.
    • Nonribosomal peptides (NRP) are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi.
    • Nonribosomal peptides are synthesized by nonribosomal peptide synthetases, which, unlike the ribosomes, are independent of messenger RNA.
    • Each nonribosomal peptide synthetase can synthesize only one type of peptide.
    • Nonribosomal peptides are synthesized by one or more specialized nonribosomal peptide-synthetase (NRPS) enzymes.

  • Antimicrobial Peptides

    • In contrast to the clonal, acquired adaptive immunity, endogenous peptide antibiotics or antimicrobial peptides provide a fast and energy-effective mechanism as front-line defense.
    • Antimicrobial peptides (AMPs) are small molecular weight proteins with broad spectrum antimicrobial activity against bacteria, viruses, and fungi.
    • Peptides of the defensin, cathelicidin, and histatin classes are found in humans .
    • Once in a target microbial membrane, the peptide kills target cells through diverse mechanisms.
    • Decreased levels of these peptides have been noted for patients with atopic dermatitis and Kostmann's syndrome, a congenital neutropenia.

  • Antimicrobial Peptides

    • Antimicrobial peptides (also called host defense peptides) are an evolutionarily conserved component of the innate immune response and are found among all classes of life.
    • Antimicrobial peptides generally consist of between 12 and 50 amino acids.
    • The initial contact between the peptide and the target organism is electrostatic, as most bacterial surfaces are anionic, or hydrophobic, such as in the antimicrobial peptide Piscidin.
    • It appears as though many peptides initially isolated and termed as "antimicrobial peptides" have been shown to have more significant alternative functions in vivo (e.g. hepcidin).
    • Several methods have been used to determine the mechanisms of antimicrobial peptide activity.

  • Protease Inhibitors

    • Proteases are enzymes that have the ability to cut proteins into peptides.
    • Protease inhibitors are short peptide-like molecules that are competitive inhibitors of the enzyme.
    • Instead of -NH-CO- peptide link, they contain -(CH2-CH(OH)-).
    • Saquinavir is the first clinically used peptide-like inhibitor.
    • Some protease inhibitors do not mimic peptides in their structure.

  • Purifying Proteins by Affinity Tag

    • Protein tags are peptide sequences genetically grafted onto a recombinant protein.
    • Protein tags are peptide sequences genetically grafted onto a recombinant protein.
    • Epitope tags are short peptide sequences which are chosen because high-affinity antibodies can be reliably produced in many different species.
    • AviTag, a peptide allowing biotinylation by the enzyme BirA and so the protein can be isolated by streptavidin (GLNDIFEAQKIEWHE)
    • Strep-tag, a peptide which binds to streptavidin or the modified streptavidin called streptactin (Strep-tag II: WSHPQFEK)

  • Phage Display

    • The bacteria process the new gene so that a new protein or peptide is made.
    • This protein or peptide is exposed on the phage surface.
    • Each phage receives only one gene, so each expresses a single protein or peptide.
    • A collection of phage displaying a population of related but diverse proteins or peptides is called a library.
    • Sequencing of the phage DNA tells the identity of the peptide that binds the target.

  • T Cell Receptors

    • T lymphocytes have a dual specificity: they recognize polymorphic residues of self major histocompatibility complex (MHC) molecules, which accounts for their MHC restriction; they also recognize residues of peptide antigens displayed by these MHC molecules, which is responsible for their specificity.
    • MHC molecules and peptides form complexes on the surface of antigen presenting cells (APCs).
    • The receptor that recognizes these peptide-MHC complexes is called the T Cell Receptor (TCR).
    • The recognition of peptide-MHC complexes is mediated by CDRs formed by both the alpha and beta chains of the TCR.

  • Classes of T Cells

    • T cells play a central role in cell-mediated immune response through the use of the surface T cell receptor to recognize peptide antigens.
    • These structures help recognize antigens only in the form of peptides displayed on the surface of antigen-presenting cells.

  • The Cell Wall of Bacteria

    • Peptidoglycan is a huge polymer of disaccharides (glycan) cross-linked by short chains of identical amino acids (peptides) monomers.
    • They are connected by inter-peptide bridges.

  • MHC Polymorphism and Antigen Binding

    • The polymorphic regions in each allele are located in the region for peptide contact, which is going to be displayed to the lymphocyte.
    • For this reason, the contact region for each allele of MHC molecule is highly variable, as the polymorphic residues of the MHC will create specific clefts in which only certain types of residues of the peptide can enter.
    • This imposes a very specific link between the MHC molecule and the peptide, and it implies that each MHC variant will be able to bind specifically only those peptides that are able to properly enter in the cleft of the MHC molecule, which is variable for each allele.
    • In this way, the MHC molecules have a broad specificity, because they can bind many, but not all, types of possible peptides.