RESUMO
The N-terminal NC4 domain of collagen IX is a globular structure projecting away from the surface of the cartilage collagen fibril. Several interactions have been suggested for this domain, reflecting its location and its characteristic high isoelectric point. In an attempt to characterize the NC4 domain in more detail, we set up a prokaryotic expression system to produce the domain. The purified 27.5-kDa product was analyzed for its glycosaminoglycan-binding potential by surface plasmon resonance and solid-state assays. The results show that the NC4 domain of collagen IX specifically binds heparin with a K(d) of 0.6 microm, and the full-length recombinant collagen IX has an even stronger interaction with heparin, with an apparent K(d) of 3.6 nm. The heparin-binding site of the NC4 domain was located in the extreme N terminus, containing a heparin-binding consensus sequence, whereas electron microscopy suggested the presence of at least three additional heparin-binding sites on full-length collagen IX. The NC4 domain was also shown to bind cartilage oligomeric matrix protein. This interaction and the association of cartilage oligomeric matrix protein with other regions of collagen IX were found to be heparin-competitive. Circular dichroism analyses of the NC4 domain indicated the presence of stabilizing disulfide bonds and a thermal denaturation point of about 80 degrees C. The pattern of disulfide bond formation within the NC4 domain was identified by tryptic peptide mass mapping of the NC4 in native and reduced states. A similar pattern was demonstrated for the NC4 domain of full-length recombinant collagen IX.
Assuntos
Cartilagem/metabolismo , Colágeno Tipo IX/química , Glicosaminoglicanos/química , Sítios de Ligação , Biotinilação , Dicroísmo Circular , Colágeno/química , Dissulfetos , Heparina/química , Humanos , Cinética , Espectrometria de Massas , Microscopia Eletrônica , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes/química , Espectroscopia de Infravermelho com Transformada de Fourier , Ressonância de Plasmônio de Superfície , Temperatura , Fatores de TempoRESUMO
We have isolated the novel gene SMOC-2, which encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain found only in the homologous SMOC-1. Phylogenetic analysis of the calcium-binding domain sequences showed that SMOC-1 and -2 form a separate group within the BM-40 family. The human and mouse SMOC-2 sequences are coded for by genes consisting of 13 exons located on chromosomes 6 and 17, respectively. Analysis of recombinantly expressed protein showed that SMOC-2 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots and reverse transcription PCR revealed a widespread expression in many tissues.
Assuntos
Proteínas de Ligação ao Cálcio/genética , Sequência de Aminoácidos , Sequência de Bases , Northern Blotting , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/metabolismo , Clonagem Molecular , DNA Complementar , Evolução Molecular , Humanos , Dados de Sequência Molecular , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência de AminoácidosRESUMO
We have isolated the novel gene SMOC-1 that encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain. Recombinant expression in human cells showed that SMOC-1 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots, reverse transcriptase-PCR, and immunoblots revealed a widespread expression in many tissues. Immunofluorescence studies with an antiserum directed against recombinant human SMOC-1 demonstrated a basement membrane localization of the protein and additionally its presence in other extracellular matrices. Immunogold electron microscopy confirmed the localization of SMOC-1 within basement membranes in kidney and skeletal muscle as well as its expression in the zona pellucida surrounding the oocyte.
