Protein Structure Levels

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∟Protein Structure Levels

This section provides a quick introduction of protein structure levels, Primary, Secondary, Tertiary and Quaternary structure levels.

What Are Protein Structure Levels? - A large protein conformation can be considered to have 4 structure levels from a construction point of view.

1. Primary Structure Level The primary structure of proteins is the protein sequence of its amino acid residues linked by peptide bonds. The primary structure of a protein is represented by a sequence of abbreviations of its linked amino acid residues. For example, the Trp-Cage protein has the following primary structure.

NLYIQWLKDGGPSSGRPPPS

2. Secondary Structure Level The secondary structure is the ordered arrangement of amino acid residues in localized regions of a protein. The two main secondary structures are the alpha helix and beta sheet. Hydrogen bondings are used to stabilize these arrangements. See next section for more details.

3. Tertiary Structure Level The tertiary structure of a protein is the three-dimensional arrangement of secondary structures of a protein. A tertiary structure is largely maintained by disulfide bonds. which are formed between the side chains of cysteine by oxidation of two thiol groups (SH) to form a disulfide bond (S-S), also sometimes called a disulfide bridge.

4. Quaternary Structure Level The quaternary structure is used to describe composed proteins (or protein complexes), which consists of multiple noncovalently-linked protein sequences. A quaternarytiary structure is mainly stabilized by hydrophobic interactions.