The spatial structure formed by the spatial arrangement of protein subunits and the interconnection between subunit secondary bonds
The fourth structure is to study the relationship and spatial location between the subunits of multibody protein moleculesProtein subunitThe spatial structure formed by the spatial arrangement of the subunit and the interconnection between the subunit secondary bonds.Each subunit has its own primary, secondary and tertiary structure. A protein composed of two or more peptide chains through non covalent bonds is called an oligoprotein.
Chinese name
Four level structure
Features
To study the relationship between multibody protein subunits
Having four levels of structureproteinComplexes can usually be described according to their subunit order, for example, two subunits are called dimers, three are trimers, and so on (those with only one protein polypeptide chain are called monomers).Generally, protein complexes in cells rarely exceed octamers.But there are some exceptions, such asProteasome(28 polymers), exosomes, spliceosomes, etc. These proteins with multiple subunits can often form molecular machines in cells to complete a specific complex biological process;VirusesThe capsid can even be 60 polymer.
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Four level structure
macromoleculeproteinIt is usually composed of multiple polypeptide chains, each of which has an independent tertiary structure.The quaternary structure of protein refers to the spatial conformation of several polypeptide chains with independent tertiary structure, which are connected and arranged in a specific way to form a higher level of macromolecular protein.In the quaternary structure of protein, each polypeptide chain with independent tertiary structure is calledSubunit。The subunits that make up the protein are mostly even numbers, which can be the same or different kinds of subunits. Different kinds of subunits are generally usedα、βThe enzyme regulatory and catalytic subunits are mostly represented by R and C.
for exampleHemoglobin moleculeThere are two, 141Amino acid residueConstituentαSubunitAnd two amino acid residuesβA subunit consisting of a specific contact and arrangementGlobular proteinMolecule, each subunit containsFerrous ionThe heme cofactor.The four subunits maintain the tight spatial conformation of hemoglobin molecules by hydrogen bonds and eight salt bonds.
With four levelsStructural proteinIn the molecule, the subunit exists alone withoutbiological activityHowever, not all protein molecules have a quaternary structure. Most proteins only have a tertiary structure and have biological activity. Only proteins with larger molecules have a quaternary structure.
determination
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compoundDirect quality analysis method
analytical ultracentrifuge
mass spectrum
Direct analysis method of composite size
Molecular exclusion chromatography
Static light scattering
Indirect analysis method of composite size
dynamic light scattering
Measurement of fluorescence anisotropy
Conformation and function
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Proteins with a quaternary structure have an allosteric effect.Allosteric action refers to the action of some physiological small molecules on a protein with a fourth order structure, combining with a part outside its active center, which can cause the breaking or formation of some bonds between its subunits, change the spatial contact and arrangement of subunits and subunits, and slightly change the conformation of the whole protein molecule, including some molecules becoming slightly loose or tight,The process of increasing or decreasing the biological activity of protein.The allosteric action of protein enables protein to continuously adjust its activity in the organism, better adapt to changes in the environment, and thus more effectively complete its physiological function, which is an important feature of the evolution of protein molecules to the level of four levels of structure.
