C4b-binding protein (C4bp) is a serum glycoprotein that is one of the regulators of the complement activation family. This multimeric protein is composed of structurally related 70-kDa (alpha chain) and 45-kDa (beta chain) polypeptides.The alpha chain of C4bp (C4bp alpha) consists of eight short consensus repeats (SCR), which constitute the amino-terminal 491 residues. Human C4bp is also one of the acute-phase reactants. Aso et al. (1991) isolated 6 genomic DNA clones covering all of the human C4bp alpha gene. This gene consists of 12 exons and spans about 40 kb. Each of the eight SCR is encoded by a single exon, except for the second SCR (SCR II), which is encoded by two separate exons, demonstrating that human C4bp alpha has a split SCR at the genomic level.
General function
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Human C4b-binding protein (C4BP) is an important regulator of the complement system that also binds and inactivates the anticoagulant vitamin K-dependent protein S. These two activities are performed by the alpha and beta chains. C4BP is present in plasma in various isoforms.
Cellular localization
Secreted
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Ovarian function
Luteolysis
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Criado-Garcia et al. (1999) suggested a role for the C4BP beta in human ovary during the healing and scar resorption processes that leads to the formation of the corpus albicans and its replacement by ovarian stroma.
Expression regulated by
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Ovarian localization
regressing corpus luteum; corpus albicans
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Follicle stages
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Criado-Garcia et al. (1999) reported that C4BP beta, but not C4BP alpha, is expressed in adult human ovary. Expression of C4BP beta was detected in all ovarian biopsies analyzed, independently of age and phase of the menstrual cycle. In situ hybridization and immunostaining analyses on cryostat sections demonstrated expression of C4BP beta in both regressing corpus luteum and corpus albicans, but not in the follicles, the corpus luteum, the ovary stroma or the vascular cells. In addition, the expression pattern of the C4BP beta mRNA resembles that described for the connective tissue that invades the degenerating corpus luteum and causes a progressive fibrosis that gradually converts it into a scar, the corpus albicans, RT-PCR and immunostaining analyses of primary cultures derived from human ovaries demonstrated the presence of fibroblast-like cells that express C4BP beta.