Abstract: Modified monomers of a Shiga toxin B-subunit (STxB) protein including at least one of: an addition of a reactive unnatural amino acid residue at the C-terminal extremity, and/or a substitution with a reactive unnatural amino acid residue at an amino acid position among Asp 3, Lys 8, Glu 10, Tyr 11, Lys 23, Lys 27, Thr 49, Lys 53, His 58, Asn 59, and Arg 69, reference made to the numbering of STxB from Shigella dysenteriae. Also relates to STxB conjugates, and oligomers, in particular pentamers, of these modified STxB proteins and STxB conjugates; as well as to compositions including the same and their use in treatment, vaccination and diagnosis methods.