Revisiting the human polypeptide GalNAc-T1 and T13 paralogs

Area of Science:

• Biochemistry
• Glycobiology
• Molecular Biology

Background:

• Polypeptide GalNAc-transferases (GalNAc-Ts) are key enzymes initiating mucin-type O-glycosylation.
• Differential regulation of the O-glycoproteome is linked to GalNAc-T isoform substrate specificities and expression patterns.

Purpose of the Study:

• To analyze the in vitro peptide substrate specificity of GalNAc-T13.
• To identify and characterize splice variants of GalNAc-T13.
• To investigate the expression of GalNAc-T13 splice variants in neuroblastoma.

Main Methods:

• In vitro glycosylation assays to determine peptide substrate specificity.
• Reverse transcription-polymerase chain reaction (RT-PCR) to analyze splice variant expression.
• Characterization of GalNAc-T13 splice variants with altered lectin domains.

Main Results:

• GalNAc-T13 exhibits peptide substrate specificity largely overlapping with the ubiquitous GalNAc-T1 isoform.
• Nine splice variants of GalNAc-T13 were identified, adding complexity to the enzyme family.
• One variant (Δ39Ex9) was inactive, while another (Ex10b) retained activity.
• Several splice variants were significantly upregulated in neuroblastoma cell lines and tumors compared to normal brain tissue.

Conclusions:

• GalNAc-T13 likely functions similarly to GalNAc-T1 in vivo regarding peptide substrates, contrary to previous findings.
• GalNAc-T13 is uniquely expressed in the brain.
• Specific GalNAc-T13 splice variants show altered expression in neuroblastoma, suggesting potential roles in tumorigenesis, although functional implications require further investigation.