Pneumococcal surface antigen A (PsaA)

Pneumococcal surface antigen A (PsaA) is a conserved 309-amino-acid bacterial lipoprotein with a molecular mass of approximately 34.5 kDa, found anchored to the membrane of *Streptococcus pneumoniae* via a lipid modification at its N-terminus. It acts as the substrate-binding component of an ATP-binding cassette (ABC) transporter, facilitating the import of essential trace metal ions such as manganese (Mn²⁺) and zinc (Zn²⁺) into the bacterium. PsaA is critical for full virulence, as deletion mutants are avirulent in mice. Its involvement in adherence to host tissues and in enabling bacterial survival under host immune pressure has made PsaA a leading candidate for inclusion in next-generation pneumococcal vaccines. Structural studies show that PsaA features a metal-binding site essential for its transporter function. Note: Pneumococcal surface antigen A (PsaA) is distinct from Pneumococcal surface protein A (PspA), another abundant and unrelated surface virulence protein in *S. pneumoniae*.

Other names

PsaAPneumococcal surface adhesin AMetal-binding lipoproteinABC-type Mn²⁺/Zn²⁺ ABC transporter substrate-binding protein

Acts as a substrate-binding component of a bacterial ABC (ATP-binding cassette) transporter, specifically importing Mn²⁺ and Zn²⁺ which are essential for bacterial physiology. Antibodies against PsaA can block its function, thereby attenuating *S. pneumoniae* virulence.