Human factor H deficiency. Mutations in framework cysteine residues and block in H protein secretion and intracellular catabolism.
The synthesis and secretion of factor H, a regulatory protein of the complement system, were studied in skin fibroblasts from an H-deficient child who has chronic hypocomplementemic renal disease. In normal fibroblasts, factor H transcripts of 4.3 and 1.8 kilobase pairs (kb) encode a 155-kDa protein containing short consensus repeat (SCR) domains 1-20 and a 45-kDa protein which contains SCRs 1-7, respectively. The patient's fibroblasts expressed normal amounts of the 4.3- and 1.8-kb messages constitutively and after tumor necrosis factor-alpha/interferon-gamma stimulation. Lysates of [35S]methionine-labeled fibroblasts from the patient contained the 155- and 45-kDa H polypeptides, but secretion of the 155-kDa protein was blocked; the 45-kDa protein was secreted with normal kinetics. The patient's plasma lacked the 155-kDa protein but contained the small form of H. Moreover, in fibroblasts the retained 155-kDa factor H protein was not degraded, even after 12 h. Immunoflourescent staining and confocal microscopic imaging of the patient's fibroblasts indicated that factor H was retained in the endoplasmic reticulum. Sequence analysis of reverse transcription-polymerase chain reaction products (the entire coding region) and genomic DNA revealed a T1679C substitution on one allele and a G2949A substitution on the other (C518R mutation in SCR 9 and C991Y mutation in SCR 16, respectively). Both mutations affect conserved cysteine residues characteristic of SCR modules and therefore predict profound changes in the higher order structure of the 155-kDa factor H protein. These data provide the first description of a molecular mechanism for factor H deficiency and yield important insights into the normal secretory pathway for this and other plasma proteins with SCR motifs.
Ault
B H
BH
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Schmidt
B Z
BZ
Fowler
N L
NL
Kashtan
C E
CE
Ahmed
A E
AE
Vogt
B A
BA
Colten
H R
HR
D000328:Adult; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000032:analysis; D037281:Calnexin; D002478:Cells, Cultured; D017242:Complement Factor H / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D016384:Consensus Sequence; D003545:Cysteine; D017931:DNA Primers; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012867:Skin / Q000378:metabolism; D014158:Transcription, Genetic
C493495:CFH protein, human; D002135:Calcium-Binding Proteins; D017931:DNA Primers; D037281:Calnexin; D017242:Complement Factor H; D003545:Cysteine