The Human Factor H-related Protein 4 (FHR-4)

doi:10.1074/jbc.272.9.5627

The Human Factor H-related Protein 4 (FHR-4)

A NOVEL SHORT CONSENSUS REPEAT-CONTAINING PROTEIN IS ASSOCIATED WITH HUMAN TRIGLYCERIDE-RICH LIPOPROTEINS*

From the Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Strasse 74, 20359 Hamburg, the
^‡ Medical Clinic, University Hospital Eppendorf, Martinistrasse 52, 20246 Hamburg, and the
^§Institute for Cell Biology and Clinical Neurobiology, University of Hamburg, Süderfeldstrasse 24, 20246 Hamburg, Germany

^¶ To whom correspondence and reprint requests should be addressed:
Bernhard Nocht Inst. for Tropical Medicine, Bernhard-Nocht-Strasse 74, D-20359 Hamburg, Germany.
Tel.: 49-40-31182-472; Fax: 49-40-31182-400.

Abstract

A novel apoprotein of an apparent molecular mass of 86 kDa in its unreduced form was identified in human triglyceride-rich lipoproteins. This protein was purified and the amino acid sequence of six proteolytic fragments was found to overlap with that of the factor H-related proteins. In parallel we identified the cDNA encoding a new complement factor H-related protein, termed FHR-4. The sequences of the new apoprotein overlapped with that of the FHR-4 protein. Similar to the previously described factor H-related proteins, FHR-4 contains a hydrophobic signal sequence followed by a stretch of five repetitive elements termed short consensus repeats. Recombinant FHR-4 protein was expressed in the baculovirus system and has an apparent molecular mass of 42 kDa. In addition a 84-kDa dimeric form of the recombinant FHR-4 was detected. Using an immunoaffinity column with antibodies raised against the recombinant FHR-4, we isolated a 86-kDa protein from human plasma. The different molecular mass of the recombinant FHR-4 and the dimeric FHR-4 in plasma is due to different carbohydrate moieties. The 86-kDa plasma protein and the novel apolipoprotein had identical mobility on SDS-polyacrylamide gel electrophoresis analysis and reacted with antisera raised against the reFHR-4 and the purified apoprotein. In conclusion, we have identified a novel factor H-related protein, FHR-4, in human plasma and demonstrate that this protein is present in triglyceride-rich lipoproteins in a dimeric form. This observation provides an intriguing new aspect on possible function(s) of this novel protein and the other factor H-related proteins.

Footnotes

↵* This work was supported by the Deutsche Forschungsgemeinschaft (DFG) in Projects Zi432/1-2 and Klinische Forschergruppe Gr258/10-1. This work is part of the doctoral thesis of J. H. at the Department of Biology at the University of Hamburg. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) X98337[GenBank].
↵¹ The abbreviations used are:

FHR

factor H-related

SCR

short consensus repeat

VLDL

very low density lipoproteins

IDL

intermediate density lipoproteins

LDL

low density lipoproteins

HDL

high density lipoproteins

ChR

chylomicron remnants

CM

chylomicrons

TG-Lp

triglyceride-rich lipoproteins

PBS

phosphate-buffered saline

PAGE

polyacrylamide gel electrophoresis

FPLC

fast protein liquid chromatography

HPLC

high performance liquid chromatography.
↵² S. Kühn, J. Hellwage, and P. F. Zipfel, unpublished data.
↵³ C. Skerka, J. Hellwage and P. F. Zipfel, manuscript in preparation.
↵⁴ P. F. Zipfel et al., manuscript in preparation.
↵⁵ U. Beisiegel, manuscript in preparation.
↵⁶ S. Kühn and P. F. Zipfel, unpublished data.
- Received June 12, 1996.
- Revision received December 3, 1996.