Protein Structure II: Tertiary and quaternary structures of proteins; Forces stabilizing tertiary structure
Protein Structure II: Tertiary and quaternary structures of proteins; Forces stabilizing tertiary structure
Tertiary structure refers to the complete three-dimensional structure of the polypeptide units of a given protein.
- Tertiary structure is formed due to interactions between side chain R group of amino acid residues present in the proteins.
- Nearly all of the polar, hydrophilic R groups are located in the surface, where they may interact with water
- The nonpolar, hydropobic R groups are usually burried inside the protein molecule
- In tertiary structure of proteins, covalent disulfide bonds form between closely aligned cysteine residues form the unique amino acid cystine.
- Tertiary structure is stabilized by non-covalent interactions such as hydrogen bonding, hydrophobic interactions, Van der Waal’s interactions and electrostatic interactions.
- Tertiary structure contains motifs and domains.
Motifs
- A small and specific combination of secondary structural elements that can be recognized in a variety of proteins are called motifs.
- Motif is also known as super fold supersecondary structure. Motif may or may not be independently stable.
- It is a folding pattern that can describe a small part of a protein or an entire polypeptide chain
- A motif can be very simple, such as two elements of secondary structure folded against each other, and represent only a small part of a protein for example βαβ motif
- A motif can also be a very elaborate structure involving scores of protein segments folded together, such as the β barrel.
Domains
Portion of a protein that has a tertiary structure of its own and perform specific function.
- Domain is a part of a polypeptide chain that is independently stable or could undergo movements as a single entity with respect to the entire protein .
- Larger polypeptides often fold into two or more domains connected by stable flexible regions of polypeptide. These domains in the protein may perform different functions.
- Domain from a large protein generally will retain its native three-dimensional structure even when separated (for example, by proteolytic cleavage) from the remainder of the polypeptide chain.
- Domains size range from about 30 to 400 amino acid residues.
- Domains are soluble in water.
- Core of the domain is built from motifs.
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