The diversity of the proline-rich domain of pneumococcal surface protein A (PspA): Potential relevance to a broad-spectrum vaccine.

•The proline rich domain (PRD) of PspA forms three distinct groups.•PRD Group 3 contains the highly conserved non-proline block (NPB).•There is no obligate association between PRD groups and alpha-helical domain clades.•Humans can make antibody to all three PRD groups.•PRD has the potential to contribute to broad spectrum pneumococcal vaccines.