Diphtheria toxin mutant protein CRM197 (CRM197)

Diphtheria toxin mutant protein CRM197 is a genetically detoxified form of diphtheria toxin produced by *Corynebacterium diphtheriae*. It differs from wild-type diphtheria toxin by a single amino acid substitution at position G52E, which abolishes its ADP-ribosyltransferase activity and thus renders it non-toxic while retaining structural similarity to the native toxin. This property makes it an ideal carrier protein for use in conjugate vaccines where it enhances immune responses against otherwise poorly immunogenic polysaccharide antigens from pathogens such as *Streptococcus pneumoniae*, *Haemophilus influenzae* type b, and *Neisseria meningitidis*. The molecule consists of one polypeptide chain (~535 amino acids; ~58 kDa) with two subunits linked by disulfide bridges. Its genetic detoxification preserves lysine residues important for efficient chemical conjugation. It has become one of the most widely used carrier proteins globally due to its safety profile and effectiveness at eliciting protective immunity when included in pediatric combination vaccines

Other names

Cross-Reactive Material 197Diphtheria CRM197 proteinCorynebacterium diphtheriae CRM197 proteinDiphtheria toxin CRM-197 mutantCRM 197 (with or without space/hyphen)Recombinant diphtheria toxin mutant (CRM197)

When used as a carrier protein: - Enhances immunogenicity of weakly antigenic polysaccharides by converting them into T-cell dependent antigens through covalent linkage. - Induces robust antibody responses against the linked antigen without causing toxicity because it lacks ADP-ribosyltransferase activity due to the G52E mutation.