Abstract
Pneumococcal cell surface-exposed choline-binding proteins (CBPs) play pivotal roles in multiple infectious processes with pneumococci. Intracellular pneumococci can be recognized at multiple steps during bactericidal autophagy. However, whether CBPs are involved in pneumococci-induced autophagic processes remains unknown. In this study, we demonstrate that CbpC from S. pneumoniae strain TIGR4 activates autophagy through an interaction with Atg14. However, S. pneumoniae also interferes with autophagy by deploying CbpC as a decoy to cause autophagic degradation of Atg14 through an interaction with p62/SQSTM1. Thus, S. pneumoniae suppresses the autophagic degradation of intracellular pneumococci and survives within cells. Domain analysis reveals that the coiled-coil domain of Atg14 and residue Y83 of the dp3 domain in the N-terminal region of CbpC are crucial for both the CbpC-Atg14 interaction and the subsequent autophagic degradation of Atg14. Although homology modeling indicates that CbpC orthologs have similar structures in the dp3 domain, autophagy induction through Atg14 binding is an intrinsic property of CbpC. Our data provide novel insights into the evolutionary hijacking of host-defense systems by intracellular pneumococci.