Structure and Function of Choline-Binding Proteins

Streptococcus pneumoniae presents four main families of surface-exposed proteins. Among them, the choline-binding protein (CBP) family is unique as it appears only in pneumococci, their bacteriophages, and their relatives. These proteins use the unique presence of phosphorylcholine in the teichoic and lipoteichoic acids of pneumococcal cell walls to anchor a wide variety of proteins displaying different functions in virulence and host–pathogen interactions. All these proteins possess a similar choline-binding module (CBM) composed of a variable number of repeats presenting a conserved sequence and structure. Advances in elucidation of the 3D structures of some members of the CBP family have revealed that CBMs play a role not only in anchoring the protein to the pneumococcal surface, but also in modulating their activities and functions, an effect associated with the structural plasticity of the repeats. This chapter reviews the present knowledge of the structure and function of the CBP family.