posted on 2024-02-22, 18:44authored byFrancesca Nonne, Lucia Dello Iacono, Sara Bertuzzi, Luca Unione, Daniela Proietti, Nathalie Norais, Immaculada Margarit, Roberto Adamo, Jesús Jiménez-Barbero, Filippo Carboni, Maria Rosaria Romano
Glycoconjugate vaccines so far licensed are generally
composed
of a native or size-reduced capsular polysaccharide conjugated to
carrier proteins. Detailed information on the structural requirements
necessary for CPS recognition is becoming the key to accelerating
the development of next-generation improved glycoconjugate vaccines.
Structural glycobiology studies using oligosaccharides (OS) complexed
with functional monoclonal antibodies represent a powerful tool for
gaining information on CPS immunological determinants at the atomic
level. Herein, the minimal structural epitope of Haemophilus
influenzae type b (Hib) CPS recognized by a functional human
monoclonal antibody (hmAb) is reported. Short and well-defined Hib
oligosaccharides originating from the depolymerization of the native
CPS have been used to elucidate saccharide–mAb interactions
by using a multidisciplinary approach combining surface plasmon resonance
(SPR), saturation transfer difference-nanomagnetic resonance (STD-NMR),
and X-ray crystallography. Our study demonstrates that the minimal
structural epitope of Hib is comprised within two repeating units
(RUs) where ribose and ribitol are directly engaged in the hmAb interaction,
and the binding pocket fully accommodates two RUs without any additional
involvement of a third one. Understanding saccharide antigen structural
characteristics can provide the basis for the design of innovative
glycoconjugate vaccines based on alternative technologies, such as
synthetic or enzymatic approaches.