• Source: Protein subunit

In structural biology, a protein subunit is a polypeptide chain or single protein molecule that assembles (or "coassembles") with others to form a protein complex.
Large assemblies of proteins such as viruses often use a small number of types of protein subunits as building blocks.
A subunit is often named with a Greek or Roman letter, and the numbers of this type of subunit in a protein is indicated by a subscript. For example, ATP synthase has a type of subunit called α. Three of these are present in the ATP synthase molecule, leading to the designation α3. Larger groups of subunits can also be specified, like α3β3-hexamer and c-ring.
Naturally occurring proteins that have a relatively small number of subunits are referred to as oligomeric. For example, hemoglobin is a symmetrical arrangement of two identical α-globin subunits and two identical β-globin subunits. Longer multimeric proteins such as microtubules and other cytoskeleton proteins may consist of very large numbers of subunits. For example, dynein is a multimeric protein complex involving two heavy chains (DHCs), two intermediate chains (ICs), two light-intermediate chains (LICs) and several light chains (LCs).
The subunits of a protein complex may be identical, homologous or totally dissimilar and dedicated to disparate tasks.
In some protein assemblies, one subunit may be a "catalytic subunit" that enzymatically catalyzes a reaction, whereas a "regulatory subunit" will facilitate or inhibit the activity. Although telomerase has telomerase reverse transcriptase as a catalytic subunit, regulation is accomplished by factors outside the protein.
An enzyme composed of both regulatory and catalytic subunits when assembled is often referred to as a holoenzyme. For example, class I phosphoinositide 3-kinase is composed of a p110 catalytic subunit and a p85 regulatory subunit. One subunit is made of one polypeptide chain. A polypeptide chain has one gene coding for it – meaning that a protein must have one gene for each unique subunit.




See also


Fusion protein
Subunit vaccine
Protein quaternary structure
Allostery
Cooperativity
Monomer




References

Kata Kunci Pencarian:

• Protein
• Reseptor terhubung protein G
• Struktur protein
• Ribosom
• Replikasi DNA
• Hemoglobin
• Inti sel
• Kromatin
• Transkripsi (genetik)
• Rantai transpor elektron
• Protein subunit
• G protein
• Subunit
• Gi alpha subunit
• Protein quaternary structure
• Subunit vaccine
• Gq alpha subunit
• Ribosome
• G protein-coupled receptor
• Heterotrimeric G protein