Streptococcus pneumoniae surface adhesin PfbA and its interaction with erythrocytes and hemoglobin.

Streptococcus pneumoniae is one of the major colonizers of human nasopharynx and its surface protein PfbA interacts with host molecules like plasmin(ogen), fibrinogen and fibronectin for colonization. Most of the binding partners of PfbA are glycoproteins. Recently we found that PfbA exhibited high affinity towards carbohydrates. It was reported that S. pneumoniae invades erythrocytes and utilizes them to evade human innate immunity. The results of this study suggested that LPXTG motif containing pneumococcal surface proteins, erythrocyte lipid rafts and erythrocyte actin remodeling are all involved in the invasion mechanism. The erythrocyte cell membrane contains different glycoproteins and glycolipids. Therefore, to find out if PfbA plays any role in erythrocyte binding, we carried out the binding studies of rPfbA49-684 with human red blood cells (RBCs) especially with its surface molecules employing ELISA and Bio Layer Interferometry. The results from these experiments show that rPfbA49-684 has a broad specificity for carbohydrates and remarkable affinity towards RBCs and in particular with extracted surface glycolipids. Further rPfbA49-684 also exhibited moderate affinity towards hemoglobin. Thus the results of the present study provide clear evidence that PfbA can interact with RBCs and this could be one of the important factors in erythrocyte invasion of S. pneumoniae.