- Globular protein
Globular proteins, or spheroproteins are one of the two main
protein classes, comprising "globe"-like proteins that are more or less soluble in aqueous solutions (where they formcolloidal solutions). This main characteristic helps distinguishing them from fibrous proteins (the other class), which are practically insoluble.Globular structure and solubility
The term globular protein is quite old (dating probably from the 19th century) and is now somewhat archaic given the hundreds of thousands of proteins and more elegant and descriptive
structural motif vocabulary. The globular nature of these proteins can be determined without the means of modern techniques, but only by usingultracentrifuge s or dynamic lightscattering techniques.The spherical structure is induced by the protein's
tertiary structure . The molecule'sapolar (hydrophobic) amino acids are bounded towards the molecule's interior whereaspolar (hydrophilic) amino acids are bound outwards, allowingdipole-dipole interaction s with thesolvent , which explains the molecule's solubility.A wide range of roles in the organism
Unlike fibrous proteins which only play a structural function, globular proteins can act as:
*Enzyme s, by catalyzing organic reactions taking place in theorganism in mild conditions and with a great specificity. Differentesterase s fulfill this role.
*Messenger s, by transmitting messages to regulate biological processes. This function is done byhormone s, i.e.insulin etc.
*Transporter s of other molecules through membranes
* Stocks ofamino acid s.
*Regulatory roles are also performed by globular proteins rather than fibrous proteins.Members
Among the most known globular proteins is
Hemoglobin , a member of theglobin protein family . Other globular proteins are theimmunoglobulin s (IgA, IgD, IgE, IgG and IgM), and alpha, beta and gamma globulins. Seeprotein electrophoresis for more information on the different globulins. Nearly all enzymes with major metabolic functions are globular in shape, as well as manysignal transduction proteins.
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