Expression Pattern and Gene Characterization ofAsporin: A NEWLY DISCOVERED MEMBER OF THE LEUCINE-RICH REPEAT PROTEIN FAMILY

Stephen P Henry,Masamine Takanosu,Tanya C Boyd,Pauline M Mayne,Heidi Eberspaecher,Wei Zhou,Benoit De Crombrugghe,Magnus Höök,Richard Mayne

doi:10.1074/jbc.m011290200

Abstract

We have discovered a new member of the class I small leucine-rich repeat proteoglycan (SLRP) family which is distinct from the other class I SLRPs since it possesses a unique stretch of aspartate residues at its N terminus. For this reason, we called the molecule asporin. The deduced amino acid sequence is about 50% identical (and 70% similar) to decorin and biglycan. However, asporin does not contain a serine/glycine dipeptide sequence required for the assembly of O-linked glycosaminoglycans and is probably not a proteoglycan. The tissue expression of asporin partially overlaps with the expression of decorin and biglycan. During mouse embryonic development, asporin mRNA expression was detected primarily in the skeleton and other specialized connective tissues; very little asporin message was detected in the major parenchymal organs. The mouse asporin gene structure is similar to that of biglycan and decorin with 8 exons. The asporin gene is localized to human chromosome 9q22-9q21.3 where asporin is part of a SLRP gene cluster that includes extracellular matrix protein 2, osteoadherin, and osteoglycin. Further analysis shows that, with the exception of biglycan, all known SLRP genes reside in three gene clusters.

Highlights

We have discovered a new member of the class: asporin (class I) small leucine-rich repeat proteoglycan (SLRP) family which is distinct from the other class I SLRPs since it possesses a unique stretch of aspartate residues at its N terminus
The small leucine-rich repeat proteoglycans1 are a group of extracellular proteins (ECM) that belong to the leucine-rich repeat (LRR) superfamily of proteins [1, 2]
We have discovered a new member of the class I subfamily of SLRPs that we have named asporin

Summary

A NEWLY DISCOVERED MEMBER OF THE LEUCINE-RICH REPEAT PROTEIN FAMILY*

Most of the SLRP proteins are proteoglycans, and the SLRP gene family has been subdivided into 3 classes based on similarities in overall amino acid sequence, spacing of cysteine residues in the N terminus, and gene structure. The class II members, fibromodulin [8], lumican [9], PRELP [10], keratocan [11], and osteoadherin [12], have a pairwise amino acid sequence identity between 37 and 55% and have a common gene structure composed of three exons. We identify a novel SLRP family member that belongs to the class I subfamily and is closely related to biglycan and decorin We have named this new SLRP asporin due to the unique aspartate stretch at the N terminus of the translated open reading frame. We have determined the mouse and human asporin gene structure and discovered that the human asporin gene is part of a SLRP gene cluster on human chromosome 9q21.3– 9q22 that contains osteoadherin, osteoglycin/mimecan, and a gene encoding another LRR-containing protein, ECM2 [42]

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION