Title : Four N-linked glycosylation
sites in human
toll-like receptor 2 cooperate to direct efficient biosynthesis and secretion
Abstract :
- Most higher organisms have a system of innate immune defense that is mediated by a group of evolutionarily related, germ line-encoded receptors , so-called Toll-like receptors
- In mammals Toll-like receptors signal in response to pathogen-associated microbial structures
- For example, Toll-like receptor 2 appears to mediate responses to bacterial peptidoglycan and acylated lipoproteins and Toll-like receptor 4 to bacterial lipopolysaccharide
- However, the structural principles that underlie recognition of these structures are poorly understood
- Toll-like receptors have leucine leucine-rich repeats in their extracellular domains and are thus believed to adopt solenoid structures, similar to that found in platelet glycoprotein Ib
- Additionally, all Toll-like receptors contain N-linked glycosylation consensus sites , and Toll-like receptor 4 requires glycosylation for function
- Toll-like receptor glycosylation is also likely to influence receptor surface representation, trafficking, and pattern recognition
- Using circular dichroism spectroscopy, we show here that purified human Toll-like receptor 2 and 4 proteins have secondary structure contents similar to glycoprotein Ib
- We have also analyzed where consensus glycosylation sites are located in the extracellular domains of other human Toll-like receptors
- We found that there are significant differences in the location and degree of conservation between sites in different Toll-like receptors
- Using site-directed mutagenesis, we have found that in Toll-like receptor 2 extracellular domain all four predicted glycosylation sites are substituted, although one site is inefficiently core-glycosylated and its removal drastically affects secretion
- The remaining Toll-like receptor 2 glycosylation sites also contribute to efficient protein secretion, albeit to a lesser degree