Different splice variants of cartilage alpha1(XI) collagen chain undergo uniform amino-terminal processing

Collagen XI is found mainly as a component of cartilage fibrils. Among the different transcripts identified by RT-PCR for the alpha1 (XI) chain, the major tissue form has been reported to be the splicing product of exons I, III and V. In this study, two other splice isoforms of the alpha1(XI) chain were identified using N-terminal sequencing. Like the major alpha1(XI) chain, the fully processed isoforms begin at Gln254 within the N-terminal domain encoded by exon I. This sequence is followed by sequences encoded by exon IIA or III. An anti-peptide antibody allowed the identification of the exon IV encoded sequence within both isoforms. Therefore, these isoforms of the alpha1(XI) chain correspond to the splicing of exons I, IIA, III, IV and V or of exons I, III, IV and V, thus presenting larger acidic sequences than the major form. They could mediate strong ionic interactions within the cartilage matrix.