Murine protein H is comprised of 20 repeating units, 61 amino acids in length.

Abstract

A cDNA library constructed from size-selected (>28 S) poly(A)+ RNA isolated from the livers of C57B10.WR mice was screened by using a 249-base-pair (bp) cDNA fragment encoding 83 amino acid residues of human protein H as a probe. Of 120,000 transformants screened, 30 hybridized with this cDNA probe. Ten positives were colonypurified, and the largest plasmid cDNA insert, MH8 (4.4 kb), was sequenced by the dideoxy chain termination method. MH8 contained the complete coding sequence for the precursor of murine complement protein factor H (3702 bp), 100 bp of 5'-untranslated sequence, 448 bp of 3'-untranslated sequence, and a polyadenylylated tail of undetermined length. Murine pre-protein H was deduced to consist of an 18-amino acid signal peptide and 1216 residues of H-protein sequence. Murine H was composed of 20 repetitive units, each about 61 amino acid residues in length. Similar repetitive units are present in the C4b binding protein, the C3b-receptor (CR1), complement factor B and C2, and in .2-glycoprotein I and the interleukin 2 receptor. This finding suggests a common evolutionary origin for regions of these proteins.Murine complement protein H, a plasma glycoprotein of p-mobility, is a cofactor for cleavage of fluid-phase C3b by the serine protease I (1-3); C3b is the major activation product of the third component of complement, C3. Protein H has also been studied in rabbits (4, 5) and humans (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) and is most fully characterized as a regulatory component of the alternative complement pathway in the latter species. Irrespective of the species of origin, protein H has been reported to have a Mr of 150,000-160,000 and a carbohydrate content between 4% and 18% by weight and to function as a cofactor for the conversion of C3b to iC3b by serine protease I. Protein H also has been shown to accelerate the dissociation of the Bb fragment of complement factor B from the alternative pathway C3 (C3bBb) and C5 (C3b2Bb) convertases.Two other proteins acting as cofactors for serine protease I-mediated cleavage of C4b (the major activation product of the fourth component of complement C4) and/or C3b have been described in humans and mice. One of these is the plasma protein C4b-binding protein (C4BP) that serves as a cofactor for conversion of C4b to iC4b (18)(19)(20)(21)(22), and the other is the C3b receptor (CR1 for complement receptor type 1). CR1 is an integral membrane glycoprotein of Mr 160,000-250,000 that acts as a cofactor for inactivation of both C4b and C3b by serine protease I (23-27).Genetic studies have shown three codominant alleles for protein H in humans (28) and two in mice (3). In humans the loci for protein H, C4BP, and CR1 are closely linked (29). This may also be the case for the corresponding proteins in the mouse. We have shown that the structural gene for protein H is located on chromosome 1 in the mouse (P. D'Eustachio, T.K., R. A. Wetsel, R. Riblett, B. Taylor, and B.F.T., unpublished work). In humans, the CR1 structural gene has been mapped to ...

A Protein with Characteristics of Factor H Is Present on Rodent Platelets and Functions as the Immune Adherence Receptor

“…Antibodies (Abs)-Goat anti-human factor H was purchased from Quidel (San Diego, CA), and cross-reacts with mouse and rat factor H (see below), which is not surprising given that factor H is highly conserved among species (20). Sheep Abs were raised to rat rCrry (21) and rDAF (22) (a gift of Dr. B. Paul Morgan, University of Wales College of Medicine, Cardiff).…”

“…Subsequent PCR was performed with 20 mM Tris-HCl, 2 mM MgCl 2 , 100 M of each deoxynucleotide triphosphate, 0.1 M of each primer, and 2.5 units of Taq polymerase. The primers were designed from the known sequence of mouse factor H, spanning bases 2556 -3028 (GenBank TM accession number M12660) (20): sense, 5Ј-TGATTGAAAC-CACCGTGAAA-3Ј and antisense 5Ј-AATAAATGCTGGTTCCATC-3Ј. Thirty cycles of 1 min denaturation at 94°C, 1 min annealing at 56°C and 1 min extension at 72°C were performed.…”

“…Tryptic peptides from the 150-kDa C3b-binding protein were analyzed by LC/MS/MS and found to be identical to the sequence of mouse factor H (20). Direct comparisons were made between the platelet 150-kDa C3b-binding protein and factor H purified from rat plasma.…”

Critical Role of the C-Terminal Domains of Factor H in Regulating Complement Activation at Cell Surfaces

“…The 20 homologous domains of factor H are each composed of ϳ60 aa with 3-8 aa spacers between the domains (29,30). In the electron microscope factor H appears to have the structure of flexible "beads on a string" (31,32).…”

Constitutive Expression and Regulation of Rat Complement Factor H in Primary Cultures of Hepatocytes, Kupffer Cells, and Two Hepatoma Cell Lines

“…FH further promotes the dissociation of the C3bBb complex (ie, it has decayaccelerating activity) (Weiler et al, 1976;Whaley and Ruddy, 1976) and prevents factor B from binding to C3b (DiScipio, 1981;Kazatchkine et al, 1979). FH consists of 1216 aa in mouse (Kristensen and Tack, 1986) and 1231 aa in man (Ripoche et al, 1988a coded. As a truncated splicing form of the FH-specific mRNA, it comprises the SCR 1-7 (Schwaeble et al, 1987(Schwaeble et al, , 1991 and is present in human serum at concentrations of 20 to 50 g/ml.…”