Peptide Basics

Peptide Basics

What are Peptides?

A peptide is a naturally occurring chemical compound found in biological systems, consisting of two or more amino acids linked together through peptide bonds. Peptide bonds are covalent connections formed when the carboxyl group (C-terminus) of one amino acid reacts with the amino group (N-terminus) of another amino acid, releasing a water molecule in the process. This results in the formation of a CO-NH bond, creating a peptide or amide molecule. Peptide bonds are essentially amide bonds.

The term “peptide” originates from the Greek word “πέσσειν,” meaning “to digest.” Peptides are fundamental components of both nature and biochemistry, with thousands naturally occurring in the human body and animals. Furthermore, laboratories continually discover and synthesize new peptides. This ongoing exploration and innovation in peptide research hold significant potential for advancements in healthcare and pharmaceutical development.

How are Peptides formed?

Peptides can originate from two sources: naturally within the body and through laboratory synthesis. The body naturally produces certain peptides, including ribosomal and non-ribosomal peptides. In laboratories, modern peptide synthesis techniques, such as liquid phase peptide synthesis or solid phase peptide synthesis, enable the creation of an almost limitless variety of peptides. Solid phase peptide synthesis is currently the preferred and standard method for peptide synthesis, although liquid phase synthesis has its advantages.

The inception of synthetic peptides dates back to 1901 when Emil Fischer, in collaboration with Ernest Fourneau, first discovered a synthetic peptide. In 1953, Vincent du Vigneaud achieved a significant milestone by synthesizing the first polypeptide, oxytocin.

Classification of Peptides

Peptides are commonly categorized into different classes based on their production methods. Ribosomal peptides are synthesized through the translation of mRNA and often serve as hormones and signaling molecules in organisms. Examples include tachykinin peptides, vasoactive intestinal peptides, opioid peptides, pancreatic peptides, and calcitonin peptides. Certain organisms produce ribosomal peptides known as antibiotics, such as microcins. These ribosomal peptides typically undergo proteolysis, the process of breaking down proteins into smaller peptides or amino acids, to reach their mature form.

In contrast, nonribosomal peptides are generated by peptide-specific enzymes rather than ribosomes. Nonribosomal peptides frequently have cyclic structures, although linear nonribosomal peptides can also exist. They are commonly found in plants, fungi, and single-celled organisms. One well-known nonribosomal peptide is glutathione, a crucial component of antioxidant defenses in aerobic organisms.

Milk peptides are derived from milk proteins and can result from enzymatic breakdown by digestive enzymes or from proteinases produced by lactobacilli during milk fermentation. Peptones, on the other hand, are peptides obtained from animal milk or meat through proteolytic digestion. Peptones are often used in laboratories as nutrients for the growth of fungi and bacteria.

Peptide fragments are typically produced through enzymatic degradation performed in controlled laboratory settings. However, they can also occur naturally through various degradation processes.

Key Peptide Terms

To better understand peptides, peptide synthesis, and their applications in research and experimentation, here are some fundamental peptide-related terms to familiarise yourself with:

  • Amino Acids: The building blocks of peptides which are composed of molecules containing both amine and carboxyl functional groups. Peptides are constructed from alpha-amino acids.

  • Cyclic Peptides: Peptides in which the amino acid sequence forms a ring structure instead of a linear chain. Examples include Melanotan-2 and PT-141 (Bremelanotide).

  • Peptide Sequence: The order in which amino acid residues are connected by peptide bonds in a peptide.

  • Peptide Bond: A covalent bond formed between two amino acids when the carboxyl group of one amino acid reacts with the amino group of another, releasing a water molecule in a condensation reaction.

  • Peptide Mapping: A method used to validate or determine the amino acid sequence of specific peptides or proteins by breaking them up with enzymes and examining the resulting amino acid sequences.

  • Peptide Mimetics: Molecules that mimic the biological activity of ligands from hormones, cytokines, enzyme substrates, viruses, or other bio-molecules. These can include natural peptides, synthetically modified peptides, or other functional molecules.

  • Peptide Fingerprint: A chromatographic pattern of a peptide produced by partially hydrolyzing the peptide to break it into fragments and then mapping those resulting fragments in two dimensions.

  • Peptide Library: A collection of numerous peptides systematically combining different amino acids. Peptide libraries are commonly used in protein research for biochemical and pharmaceutical purposes, with solid phase peptide synthesis being the primary technique for their preparation

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