The structure of type IX collagen.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Previous isolation of high molecular weight (HMW) and low molecular weight (LMW) collagenous fragments from chicken cartilage.
• Limited understanding of the subunit composition and structure of these fragments.

Purpose of the Study:

• To perform a detailed analysis of tryptic peptides and amino-terminal sequences of HMW and LMW fragments.
• To compare these findings with the nucleotide sequence of cDNApYN1738.
• To characterize a unique collagen type from chicken cartilage.

Main Methods:

• Tryptic peptide analysis of collagen fragments.
• Amino-terminal sequencing of collagen subunits.
• Comparison with existing cDNA nucleotide sequences (cDNApYN1738).

Main Results:

• HMW and LMW fragments are pepsin-resistant parts of a unique collagen.
• This collagen, designated Type IX collagen, has three different polypeptide chains (alpha-chains).
• The alpha-chain encoded by pYN1738 is designated alpha 1 (IX).
• Type IX collagen possesses three triple-helical domains and interchain disulfide bridges.
• Noncollagenous domains at amino and carboxyl ends are not homologous to interstitial collagen propeptides.

Conclusions:

• Identification and characterization of Type IX collagen as a distinct collagen type.
• Elucidation of the subunit composition and domain structure of Type IX collagen.
• Type IX collagen represents a novel structural class of collagen with unique features.