Chemical Synthesis and Immunological Evaluation of Archaeal Rare Sugar L-TalNAcA and Its Derivatives

Human-associated archaea, such as Methanobrevibacter smithii and Methanosphaera stadtmanae, have attracted increasing attention for their potential involvement in the modulation of host immune responses. However, the molecular mechanisms underlying these interactions remain poorly understood. Pseudopeptidoglycan (pPG), a major component of the archaeal cell wall, is a potential mediator of such immunomodulatory effects. Although N-acetyl-L-talosaminuronic acid (L-TalNAcA) has been proposed as a constituent of pPG, both its precise structural context within the archaeal cell wall and the immunological properties of its glycoconjugates remain largely unexplored. In this study, we established a synthetic route to L-TalNAcA and its derivatives, including mono- and disaccharide glycopeptides. LC-MS/MS analysis using synthetic L-TalNAcA as a reference standard supported the presence of this rare sugar in archaeal cell wall hydrolysates. Furthermore, immunological evaluation using reporter cell lines revealed that the M. smithii-type monosaccharide glycopeptide induced hNOD2-dependent activation. These findings provide molecular evidence of host receptor recognition of an archaeal cell wall-related glycopeptide motif and establish a chemical platform for further investigating archaeal-host immune interactions.