Biology:Protein subunit
In structural biology, a protein subunit is a single protein molecule that assembles (or "coassembles") with other protein molecules to form a protein complex. Some naturally occurring proteins have a relatively small number of subunits and therefore described as oligomeric, for example hemoglobin or DNA polymerase. Others may consist of a very large number of subunits and therefore described as multimeric, for example microtubules and other cytoskeleton proteins. The subunits of a multimeric protein 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.[1] 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.[2] 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.
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, and is therefore designated α3. Larger groups of subunits can also be specified, like α3β3-hexamer and c-ring.
Subunit vaccines
See also
- Protein quaternary structure
- Allostery
- Cooperativity
- Monomer
References
- ↑ "Regulation of the human catalytic subunit of telomerase (hTERT)". Gene 498 (2): 135–46. 2012. doi:10.1016/j.gene.2012.01.095. PMID 22381618.
- ↑ "Purification and characterization of phosphoinositide 3-kinase from rat liver". J. Biol. Chem. 265 (32): 19704–11. November 1990. doi:10.1016/S0021-9258(17)45429-9. PMID 2174051.
- Dilip Gore; Reecha Pandit (2011). "In silico Identification of Cell Surface Antigens in Neisseria meningitidis". Biomirror 2: 1–5.
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