Further Characterization of Proteins Associated with Elastic Fiber Microfibrils Including the Molecular Cloning of MAGP-2 (MP25)

doi:10.1074/jbc.271.2.1096

Further Characterization of Proteins Associated with Elastic Fiber Microfibrils Including the Molecular Cloning of MAGP-2 (MP25) (*)

From the (1)Department of Pathology, University of Adelaide, Adelaide, South Australia 5005, Australia
(2)Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, Adelaide, South Australia, 5006 Australia, and
(3)Pettis Memorial Veterans Hospital, Loma Linda, California 92367

^§ To whom correspondence should be addressed:
Dept. of Pathology, University of Adelaide, South Australia, 5005.
Tel.: 61-8-303-5385; Fax: 61-8-303-4408; mgibson{at}medicine.adelaide.edu.au.

Abstract

Together with the 31-kDa microfibril-associated glycoprotein (MAGP), four polypeptides designated MP340 (340 kDa), MP78 (78 kDa), MP70 (70 kDa), and MP25 (25 kDa) have previously been identified in tissue extracts designed specifically to solubilize the microfibrillar component of elastic fibers. In the present study, both MP78 and MP70 were shown to be forms of a protein which is closely related to the human protein βig-h3, and MP340 was confirmed to be the bovine form of fibrillin-1. Peptide sequences from MP25 proved to be unique, and affinity-purified anti-MP25 antibodies were shown, by immunofluorescence and immunoelectron microscopy, to localize specifically to the elastin-associated microfibrils. This confirmed that MP25 was a distinct component of these structures. Expression screening of nuchal ligament cDNA libraries yielded a cDNA, cM10A (770 base pairs) which encodes amino acid sequences matching those of the MP25 peptides. Further library screening with cM10A identified cDNAs which encode the complete primary structures of bovine and human MP25. Bovine and human MP25 were found to be around 80% homologous and contain 170 and 173 amino acids, respectively. Data base searches revealed that MP25 had significant similarity of structure only with MAGP, indicating that the two proteins form a new family of microfibrillar proteins. In acknowledgment, MP25 has been formally renamed MAGP-2, and MAGP is referred to as MAGP-1. The close similarity between the two proteins (57%) is confined to a central region of 60 amino acids where there is precise alignment of 7 cysteine residues. Elsewhere the MAGP-2 molecule is rich in serine and threonine residues and contains an RGD motif. MAGP-2 lacks the proline-, glutamine-, and tyrosine-rich sequences and a hydrophobic carboxyl terminus, characteristic of MAGP-1. These structural differences suggest that MAGP-2 has some functions which are distinct from those of MAGP-1. The locus of the human MAGP-2 gene was identified on chromosome 12 in the region of 12p12.3-12p13.1.

Footnotes

↵* This work was supported by the National Health and Medical Research Council of Australia and the J. H. and J. D. Gunn Medical Research Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by 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) Bos taurus U37282[GenBank], Homo sapiens U37283[GenBank].
↵¹ The abbreviations used are:

MAGP

microfibril-associated glycoprotein

DIG

digoxigenin

MFAP

microfibril-associated protein

MP

microfibrillar protein

PAGE

polyacrylamide gel electrophoresis

bp

base pair(s)

kb

kilobase pair(s).
↵²M. A. Gibson, J. Kumaratilake, and E. G. Cleary, manuscript in preparation.
- Received July 17, 1995.
- Revision received October 9, 1995.