Complement component 1 Q subcomponent-binding protein, mitochondrial is a protein that in humans is encoded by the C1QBP gene. [5] [6] [7]
The human complement subcomponent C1q associates with C1r and C1s in order to yield the first component of the serum complement system. The protein encoded by this gene is known to bind to the globular heads of C1q molecules and inhibit C1 activation. This protein has also been identified as the p32 subunit of pre-mRNA splicing factor SF2, as well as a hyaluronic acid-binding protein. [7]
C1QBP is 282 amino acid in length and has three homologous subunit with its N-terminal 73 amino acid residues cleaved off to produce mature C1QBP. C1QBP appears as a monomer around 33 kDa on SDS-PAGE gel under both reducing and nonreducing condition but migrates as a trimer on size-exclusion chromatography (gel filtration). [8]
The crystal structure of C1QBP at 2.25 Å resolution shows a homotrimeric ring displaying symmetry. The individual subunits are held together by noncovalent interactions and forms a doughnut shaped quaternary structure with a central cavity of 20 Å in diameter. Each Subunit of C1QBP has seven β-strand (β1- β7) and three α-helices (α1- α3). C1QBP is negatively charged on its soluble face while the membrane face is predominantly positively charged. [9]
C1QBP has been shown to interact with Protein kinase D1, [10] BAT2, [11] PRKCD, [10] PKC alpha [10] and Protein kinase Mζ. [10] Other interacting partners of C1QBP include protein domains from pathogens such as bacteria, [12] virus [13] and plasmodium falciparum. [14] Plasma proteins including fibrinogen, FXII and HK have been demonstrated to interact with C1QBP in a zinc dependent manner,. [15] [16] Recently, a tumour homing peptide, LyP-1(CGNKRTRGC) has been shown to selectively bind to C1QBP in tumour expressing cells. [17]
Ku80 is a protein that, in humans, is encoded by the XRCC5 gene. Together, Ku70 and Ku80 make up the Ku heterodimer, which binds to DNA double-strand break ends and is required for the non-homologous end joining (NHEJ) pathway of DNA repair. It is also required for V(D)J recombination, which utilizes the NHEJ pathway to promote antigen diversity in the mammalian immune system.
Serine/threonine-protein phosphatase PP1-alpha catalytic subunit is an enzyme that in humans is encoded by the PPP1CA gene.
GRB2-associated-binding protein 1 is a protein that in humans is encoded by the GAB1 gene.
Calcium/calmodulin-dependent protein kinase type IV is an enzyme that in humans is encoded by the CAMK4 gene.
Nuclear transcription factor Y subunit beta is a protein that in humans is encoded by the NFYB gene.
DNA replication licensing factor MCM4 is a protein that in humans is encoded by the MCM4 gene.
Guanine nucleotide-binding protein G(q) subunit alpha is a protein that in humans is encoded by the GNAQ gene. Together with GNA11, it functions as a Gq alpha subunit.
Histone acetyltransferase KAT2A is an enzyme that in humans is encoded by the KAT2A gene.
Calcium/calmodulin-dependent protein kinase type II gamma chain is an enzyme that in humans is encoded by the CAMK2G gene.
Serine/threonine-protein kinase D1 is an enzyme that in humans is encoded by the PRKD1 gene.
5'-AMP-activated protein kinase catalytic subunit alpha-1 is an enzyme that in humans is encoded by the PRKAA1 gene.
Splicing factor U2AF 35 kDa subunit is a protein that in humans is encoded by the U2AF1 gene.
Collagen alpha-6(IV) chain is a protein that in humans is encoded by the COL4A6 gene.
Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2 is a protein that in humans is encoded by the GNG2 gene.
Eukaryotic translation initiation factor 2 subunit 2 (eIF2β) is a protein that in humans is encoded by the EIF2S2 gene.
Guanine nucleotide-binding protein subunit beta-5 is a protein that in humans is encoded by the GNB5 gene. Alternatively spliced transcript variants encoding different isoforms exist.
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Dual specificity protein kinase CLK1 is an enzyme that in humans is encoded by the CLK1 gene.
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Gamma-aminobutyric acid receptor subunit rho-1 is a protein that in humans is encoded by the GABRR1 gene.