Thermodynamic Analysis of Interactions between N-Linked Sugar Chains and F-Box Protein Fbs1

Fbs1 is a recently discovered F-box protein that was proposed to recognize high-mannose-type asparagine-linked glycoprotein sugar chains. To reveal the specificity of Fbs1, Manα1→6Manβ1→4GlcNAc₂, Manα1→3Manβ1→4GlcNAc₂, and Manα1→3(Manα1→ 6)Manβ1→4GlcNAc₂ were synthesized and their affinities for Fbs1 were evaluated in comparison with previously synthesized Man₉GlcNAc₂ and Man₈GlcNAc₂. These analyses revealed that Man₃GlcNAc₂ had the strongest affinity and the chitobiose and α1→6 linked Man residue are necessary for Fbs1 to recognize a sugar.