Claustrin, an antiadhesive neural keratan sulfate proteoglycan, is structurally related to MAP1B

Abstract

Our laboratory has recently identified a keratan sulfate proteoglycan (KSPG), named claustrin, that inhibits neural cell adhesion and neurite outgrowth in the chick nervous system. Antisera prepared against claustrin were used to screen a cDNA expression library from embryonic day 9 chick brain. Initial characterization of positive cDNAs revealed a high degree of homology to the mouse MAP1B gene, although these cDNAs represent a 5' truncated fragment of MAP1B. Protein sequencing of three peptides derived from a tryptic digest of purified, keratanase-treated claustrin also revealed strong homology to MAP1B, and confirmed the authenticity of the 3.4 kb claustrin cDNA. To further determine the relationship between these two proteins, we used antibodies against MAP1B and KSPGs in immunoblotting and immunohistochemical studies. These studies demonstrated cross-reactivity between MAP1B and claustrin antibodies, and that monoclonal antibodies to cartilage keratan sulfate react with MAP1B in rat nervous tissue, and with claustrin in the chick nervous system. In addition, keratanase treatment of a taxol microtubule fraction from chick or rat brain eliminated MAP1B, as detected by immunoblotting with the MAP5 monoclonal antibody. These results suggest that MAP1B and claustrin are highly related, if not identical, proteins.

High Molecular Weight Microtubule-associated Proteins Contain O-Linked N-Acetylglucosamine

“…In addition, claustrin was shown to incorporate While these results were interpreted as cross-reaction of these MAP antibodies with a distinct extracellular glycoprotein, it is also possible that the sulfoglycoprotein antigen detected in the extracellular matrix was a secreted form of MAP. This would correlate with the hypothesis that the keratin sulfate-containing proteoglycan claustrin might represent a secreted form of MAP1B (24). It has also been suggested that MAP1B may exist as a transmembrane cell-surface protein in rat cortical cell cultures and may be involved in synaptogenesis (32).…”

“…In addition, it has also been reported that claustrin, a chicken brain homologue of MAP1B, is a keratan sulfate-containing protein (24). Furthermore, it was shown that rat brain MAP1B is also sensitive to keratanase digestion, which hydrolyzes the ␤-galactosidic linkages present in keratan sulfate.…”

Developmental expression of keratan sulfate-like immunoreactivity distinguishes thalamic nuclei and cortical domains

“…Notably, claustrin is a 320-kD proteoglycan with only KS GAGs that is reportedly recognized by 5D4 (Cole and McCabe, 1991). In addition, claustrin has been localized to the subplate and marginal zone of E20 rat forebrain (Burg and Cole, 1993). However, very different profiles are evident on Western blots of rat brain homogenates immunolabeled with a polyclonal antibody to claustrin or with 5D4 (Fig.…”

“…Furthermore, in our hands, the antibody to claustrin labels E16 cortex diffusely (data not shown), a pattern not seen with 5D4. Claustrin is sensitive to keratanase I digestion (Burg and Cole, 1993), unlike the 5D4 epitope. Thus, although 5D4 may recognize KS associated with claustrin (Cole and McCabe, 1991), our results suggest that the bulk of KS recognized by 5D4 and reported here is not associated with claustrin.…”

Keratan Sulfate in Neuronal Network Reconstruction

“…Interestingly, these activities are reversed by enzymatic digestion of KS or anti-KS monoclonal antibody. It has also been reported that claustrin is an N-terminal truncated form of MAP1B, and that MAP1B is itself a KSPG (18,19). It still remains unclear how signal peptide-less proteins such as MAP1B and claustrin are secreted as KSPGs.…”