Streptococcus pneumoniae Binds to Host Lactate Dehydrogenase via PspA and PspC To Enhance Virulence

Abstract

Pneumococcal surface protein A (PspA) and pneumococcal surface protein C (PspC, also called CbpA) are major virulence factors of Streptococcus pneumoniae (Spn). These surface-exposed choline-binding proteins (CBPs) function independently to inhibit opsonization, neutralize antimicrobial factors, or serve as adhesins. PspA and PspC both carry a proline-rich domain (PRD) whose role, other than serving as a flexible connector between the N-terminal and C-terminal domains, was up to this point unknown. Herein, we demonstrate that PspA binds to lactate dehydrogenase (LDH) released from dying host cells during infection. Using recombinant versions of PspA and isogenic mutants lacking PspA or specific domains of PspA, this property was mapped to a conserved 22-amino-acid nonproline block (NPB) found within the PRD of most PspAs and PspCs. The NPB of PspA had specific affinity for LDH-A, which converts pyruvate to lactate. In a mouse model of pneumonia, preincubation of Spn carrying NPB-bearing PspA with LDH-A resulted in increased bacterial titers in the lungs. In contrast, incubation of Spn carrying a version of PspA lacking the NPB with LDH-A or incubation of wild-type Spn with enzymatically inactive LDH-A did not enhance virulence. Preincubation of NPB-bearing Spn with lactate alone enhanced virulence in a pneumonia model, indicating exogenous lactate production by Spn-bound LDH-A had an important role in pneumococcal pathogenesis. Our observations show that lung LDH, released during the infection, is an important binding target for Spn via PspA/PspC and that pneumococci utilize LDH-A derived lactate for their benefit in vivo. IMPORTANCE Streptococcus pneumoniae (Spn) is the leading cause of community-acquired pneumonia. PspA and PspC are among its most important virulence factors, and these surface proteins carry the proline-rich domain (PRD), whose role was unknown until now. Herein, we show that a conserved 22-amino-acid nonproline block (NPB) found within most versions of the PRD binds to host-derived lactate dehydrogenase A (LDH-A), a metabolic enzyme which converts pyruvate to lactate. PspA-mediated binding of LDH-A increased Spn titers in the lungs and this required LDH-A enzymatic activity. Enhanced virulence was also observed when Spn was preincubated with lactate, suggesting LDH-A-derived lactate is a vital food source. Our findings define a role for the NPB of the PRD and show that Spn co-opts host enzymes for its benefit. They advance our understanding of pneumococcal pathogenesis and have key implications on the susceptibility of individuals with preexisting airway damage that results in LDH-A release.

Streptococcus pneumoniae binds to host GAPDH on dying lung epithelial cells worsening secondary infection following influenza

“…The ability of PspA to mediate bacterial attachment to dying cells is perhaps the most straightforward explanation for how it contributes to enhanced pneumonia severity. We speculate that in addition to helping the bacteria avoid mucociliary clearance, the close physical interaction of Spn with dying lung cells also serves to enhance the bacterium’s accessibility to any released nutrients or host proteins that could be co-opted by Spn ( Park et al, 2021 ; Sender et al, 2020 ). These would otherwise be diluted within the mucosal secretions.…”

A Jack of All Trades: The Role of Pneumococcal Surface Protein A in the Pathogenesis of Streptococcus pneumoniae

“…In our studies that identified PspA as having affinity to lactate dehydrogenase and GAPDH, it was observed that PspA also had affinity to numerous other host proteins (Park et al, 2021a;Park et al, 2021b). Among these was the filamentous protein vimentin, which has been implicated as a key ligand for group B Streptococci and E. coli with regard to their ability to gain access to the central nervous system (Deng et al, 2019).…”

“…Curates PC residues on pneumococcal surface (Gosink et al, 2000;Hermoso et al, 2005) Choline McDaniel et al, 1986;McDaniel et al, 1987;Shaper et al, 2004;Mukerji et al, 2012;Park et al, 2021a;Park et al, 2021b) Pneumococcal choline-binding protein A…”

“…PspA showed comparably stronger affinity towards human lactoferrin compared to that from other species Mukerji et al, 2018). The PRD composition of PspA from TIGR4, GA44128 and WU2 strains representing each group of PRD are shown in inset (adapted from Park et al, 2021a). (Hammerschmidt et al, 1999).…”

“…With exception to serotype 1 ( Cornick et al., 2017 ), the majority of Spn produce pneumococcal surface protein A (PspA), a 65 to 99-kDa CBP that protects the bacteria from C-reactive protein-mediated activation of complement and from killing by lactoferricin, a cationic antimicrobial peptide ( Hammerschmidt et al., 1999 ; Tu et al., 1999 ). Recent findings from our group describe two new functions for PspA, as an adhesin and means to co-opt host metabolic enzymes for its benefit ( Park et al., 2021a ; Park et al., 2021b ). Indeed, this protein acts as a “Jack of All Trades.” In this review, we will summarize how PC and CBPs contribute to pneumococcal pathogenesis and the role PspA plays during infection.…”