Alternative mRNA Processing Occurs in the Variable Region of the Pro-α1(XI) and Pro-α2(XI) Collagen Chains

Abstract

An analysis was performed of differential splicing of primary transcripts in the noncollagenous variable region located in the amino terminus of the pro-alpha 1(XI) and pro-alpha 2(XI) collagen chains. The results for the pro-alpha 2(XI) chain showed that human cartilage or fibroblasts in culture contain transcripts in which a single highly acidic exon encoding for 21 amino acids is present or absent. For the chicken pro-alpha 1(XI) chain a more complex pattern of alternative splicing was detected with six possible variants. Of special interest was the alternative use of two exons (called IIA and IIB) in which IIA encodes for 39 amino acids and is highly acidic (estimated pI = 3.2), whereas IIB encodes for 49 amino acids and is highly basic (estimated pI = 10.6). A similar alternative use of exon IIA or exon IIB was also observed for human chondrocytes. Northern blotting with probes specific for IIA or IIB showed that both exons are present in transcripts from cartilage but exon IIB is preferentially utilized in transcripts from tendon. Present results suggest that both the pro-alpha 1(XI) and pro-alpha 2(XI) chains of type XI collagen undergo limited processing in vivo and that the noncollagenous variable region is initially retained on the surface of the fibrils. Differential splicing in the variable region may potentially influence the interaction of collagen fibrils with other molecules of the extracellular matrix and more specifically with sulfated glycosaminoglycan chains or with hyaluronan. Such interactions may play a key role in establishing both the organization of the collagen fibrils within the extracellular matrix and in limiting the diameter of collagen fibrils.

Macromolecular Specificity of Collagen Fibrillogenesis

“…1, lane 1). This complex polypeptide composition results from both alternative splicing (37,38) as well as incomplete proteolytic processing of the amino-terminal propeptide domain (39,40). Collagen I was purified by ion exchange chromatography on DEAE-cellulose from a mixture of collagens extracted from leg tendons of 17-day-old chicken embryos.…”

Ubiquitous Expression of the α1(XIX) Collagen Gene (Col19a1) during Mouse Embryogenesis Becomes Restricted to a Few Tissues in the Adult Organism

“…Alternative splicing has been reported to occur for several different collagen types (17)(18)(19)(20)(21)(22)(23)(24), although its functional significance is understood only for a few of them. In the case of the ␣1(XIX) chain, the results are apparently contradictory.…”

Expression, purification, and refolding of recombinant collagen α1(XI) amino terminal domain splice variants

“…This is in contrast to the α1(XI) NTD[p6a+8] splice variant reported previously, which demonstrated a decrease in content of ordered structure when compared to α1(XI) Npp [14]. Exon 6b is rich in codons for the positively charged amino acids arginine and lysine, which significantly alter the theoretical isoelectric point (pI) from 5.75 (α1(XI) NTD[p7]) to 9.19 (α1(XI) NTD[p6+7]) [28], [10], and [13]. Proteins high in β-strand and β-turns are often difficult to denature and refold effectively without aggregation.…”

“…The variable region, which spans exons 6a, 6b, 7, 8 and 9, encodes several biochemically unique domains (Fig. 1A) which are expressed in a manner that includes alternative splicing at the mRNA level, resulting in expression of different protein splice variants [10]. The most abundant forms of the α1 chain of type XI collagen are α1(XI) NTD[p7] and α1(XI) NTD[p6b+7] comprising 40% and 30% of expressed α1(XI) respectively (Fig.…”