Protein G
Encyclopedia
Protein G is an immunoglobulin-binding protein expressed in group C and G Streptococcal bacteria much like Protein A
but with differing specificities. It is a 65-kDa (G148 protein G) and a 58 kDa (C40 protein G) cell surface protein that has found application in purifying antibodies through its binding to the Fc region. The native molecule also binds albumin, however, because serum albumin is a major contaminant of antibody sources, the albumin binding site has been removed from recombinant
forms of Protein G.
The Sequence of protein G is :
SOURCE
ORIGIN
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pI:Results from "EMBL WWW Gateway to Isoelectric Point Service"
Isoelectric Point: 6.01499999999989 (using a ph increment of 0.005 for the calculation of the lowest net charge. Charge at that pH is 1.11022302462516e-16)
, Protein A/G
and Protein L
are all commonly used to purify, immobilize or detect immunoglobulins. Each of these immunoglobulin-binding proteins has a different antibody binding profile in terms of the portion of the antibody that is recognized and the species and type of antibodies it will bind.
of the protein G B1 domain demonstrates that, as earlier results suggested, this protein initiates folding via a nucleation
event in the hydrophobic
core residues
followed by small adjustments. The folding events are as follows:
The protein G B1 domain is (aka. GB1) often used as part of a fusion protein
to keep other domains in solution during experiments in solution (e.g. NMR
). Many previously insoluble domains have become soluble with the fusion of the GB1 domain. The domain is 56 residues (approx 8kDa) long. On SDS-PAGE
gels the GB1 domain runs at roughly 13.5kDa despite being only 8kDa.
Protein A
Protein A is a 40-60 kDa MSCRAMM surface protein originally found in the cell wall of the bacterium Staphylococcus aureus. It is encoded by the spa gene and its regulation is controlled by DNA topology, cellular osmolarity, and a two-component system called ArlS-ArlR. It has found use in...
but with differing specificities. It is a 65-kDa (G148 protein G) and a 58 kDa (C40 protein G) cell surface protein that has found application in purifying antibodies through its binding to the Fc region. The native molecule also binds albumin, however, because serum albumin is a major contaminant of antibody sources, the albumin binding site has been removed from recombinant
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
forms of Protein G.
The Sequence of protein G is :
SOURCE
- 1..480
- /organism="Streptococcus sp."
- /strain="G 148"
ORIGIN
- 1 efnkygvsdy yknlinnakt vegvkdlqaq vvesakkari seatdglsdf lksqtpaedt
- 61 vksielaeak vlanreldky gvsdyhknli nnaktvegvk dlqaqvvesa kkariseatd
- 121 glsdflksqt paedtvksie laeakvlanr eldkygvsdy yknlinnakt vegvkalide
- 181 ilaalpktdt yklilngktl kgettteavd aataekvfkq yandngvdge wtyddatktf
- 241 tvtekpevid aseltpavtt yklvingktl kgettteavd aataekvfkq yandngvdge
- 301 wtyddatktf tvtekpevid aseltpavtt yklvingktl kgetttkavd aetaekafkq
- 361 yandngvdgv wtyddatktf tvtemvtevp gdaptepekp easiplvplt patpiakdda
- 421 kkddtkkeda kkpeakkeda kkaetlpttg egsnpfftaa alavmagaga lavaskrked
//
pI:Results from "EMBL WWW Gateway to Isoelectric Point Service"
Isoelectric Point: 6.01499999999989 (using a ph increment of 0.005 for the calculation of the lowest net charge. Charge at that pH is 1.11022302462516e-16)
Other antibody binding proteins
In addition to Protein G, other immunoglobulin-binding bacterial proteins such as Protein AProtein A
Protein A is a 40-60 kDa MSCRAMM surface protein originally found in the cell wall of the bacterium Staphylococcus aureus. It is encoded by the spa gene and its regulation is controlled by DNA topology, cellular osmolarity, and a two-component system called ArlS-ArlR. It has found use in...
, Protein A/G
Protein A/G
Protein A/G is a recombinant fusion protein that combines IgG binding domains of both Protein A and Protein G. Protein A/G contains four Fc binding domains from Protein A and two from Protein G, yielding a final mass of 50,460 daltons...
and Protein L
Protein L
Protein L was first isolated from the surface of bacterial species Peptostreptococcus magnus and was found to bind immunoglobulins through L chain interaction, from which the name was suggested. It consists of 719 amino acid residues...
are all commonly used to purify, immobilize or detect immunoglobulins. Each of these immunoglobulin-binding proteins has a different antibody binding profile in terms of the portion of the antibody that is recognized and the species and type of antibodies it will bind.
Folding of Protein G, B1 Domain
An ab initio simulationAb initio quantum chemistry methods
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term ab initiowas first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene.The background is described by Parr...
of the protein G B1 domain demonstrates that, as earlier results suggested, this protein initiates folding via a nucleation
Nucleation
Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form by way of nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...
event in the hydrophobic
Hydrophobe
In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
core residues
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
followed by small adjustments. The folding events are as follows:
- a β-hairpinBeta hairpinThe beta hairpin structural motif is the simplest protein motif involving two beta strands that look like a hairpin. The motif consists of two strands that are adjacent in primary structure oriented in an antiparallel arrangement and linked by a short loop of two to five amino acids...
is formed, stabilized by residues W43, Y45, and F52. - Residue contacts between residue F30, in an α-helixAlpha helixA common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
, and the β-hairpin strengthen. - Nucleation of the β-sheetBeta sheetThe β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...
starting from residues L5 and F52, occurs. - The last nucleation residue, Y3, assists in forming the central part of the β-sheet resulting in a globular proteinGlobular proteinGlobular proteins, or spheroproteins are one of the two main protein classes, comprising "globe"-like proteins that are more or less soluble in aqueous solutions...
.
The protein G B1 domain is (aka. GB1) often used as part of a fusion protein
Fusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...
to keep other domains in solution during experiments in solution (e.g. NMR
NMR
NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...
). Many previously insoluble domains have become soluble with the fusion of the GB1 domain. The domain is 56 residues (approx 8kDa) long. On SDS-PAGE
SDS-PAGE
SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis, describes a collection of related techniques widely used in biochemistry, forensics, genetics and molecular biology to separate proteins according to their electrophoretic mobility...
gels the GB1 domain runs at roughly 13.5kDa despite being only 8kDa.