Protein D (Haemophilus influenzae) (PD)

Protein D (PD) is a highly conserved, 42-kDa surface lipoprotein found in both encapsulated and non-typeable strains of Haemophilus influenzae (NTHi) (UniProt: P17944). It functions biologically as a glycerophosphodiester phosphodiesterase (GlpQ), an enzyme that plays a critical role in the acquisition of choline from host tissues, which is essential for the synthesis of the bacterial cell wall and lipooligosaccharides (PubMed: 12670935). Beyond its metabolic role, Protein D acts as a virulence factor by promoting bacterial adhesion to human respiratory epithelial cells, thereby facilitating colonization and infection (PubMed: 10858233). NTHi is a leading cause of localized respiratory infections such as acute otitis media in children and is a major driver of exacerbations in patients with chronic obstructive pulmonary disease (COPD) (PubMed: 25135305). Due to its high conservation across strains and its role in pathogenesis, Protein D has been utilized as a vaccine antigen and a carrier protein in conjugate vaccines, most notably the 10-valent pneumococcal conjugate vaccine (Synflorix) (PubMed: 19126381). Vaccination targeting Protein D aims to induce opsonophagocytic antibodies that neutralize the enzyme's activity and prevent bacterial attachment, offering a dual strategy for preventing both pneumococcal and NTHi-related diseases (PubMed: 24106296).

Other names

Glycerophosphodiester phosphodiesteraseGlpQhpdLipoprotein DNTHi surface protein PDNon-typeable Haemophilus influenzae Protein D

Induction of protective opsonophagocytic antibodies and inhibition of bacterial adherence to host cells.