Structural and functional features of a developmentally regulated lipopolysaccharide-binding protein

Area of Science:

• Microbiology
• Evolutionary Biology
• Biochemistry

Background:

• Mammalian lipopolysaccharide (LPS)-binding proteins (LBPs) primarily function in host defense by delivering LPS to cell receptors.
• The role of LBPs in nonpathogenic host-microbe interactions remains poorly understood.
• The Euprymna scolype-Vibrio fischeri symbiosis offers a model to study these interactions.

Purpose of the Study:

• To investigate the structure and function of E. scolopes LBP1 (EsLBP1) in the context of host-microbe symbiosis.
• To determine the role of EsLBP1 in mediating the symbiont-induced developmental program of the host.
• To explore the evolutionary divergence of LBPs in symbiotic interactions.

Main Methods:

• Computational modeling of EsLBP1 structure.
• Recombinant EsLBP1 expression and binding assays with various bacterial components (LPS, LOS, PGN).
• Quantitative analysis of eslbp1 transcript levels via qPCR.
• Localization of eslbp1 transcript and protein using HCR-FISH and ICC.

Main Results:

• EsLBP1 shares some structural similarities with mammalian LBPs but differs in key residues.
• Recombinant EsLBP1 bound V. fischeri LPS and N. meningitidis LOS but not F. tularensis LPS or PGN monomer.
• Symbiotic colonization by V. fischeri upregulated eslbp1 expression, surprisingly induced by PGN monomer alone, not LPS.
• EsLBP1 was localized to crypt epithelia, the site of V. fischeri-induced morphogenesis.

Conclusions:

• EsLBP1 plays a crucial role in initiating a symbiont-induced developmental program in the host.
• The induction of eslbp1 by PGN monomer suggests a distinct mechanism compared to mammalian LBP-LPS interactions.
• These findings provide insights into the evolution of LBPs and their expanded roles in animal symbioses.