The baseplate of Lactobacillus delbrueckii bacteriophage Ld17 harbors a glycerophosphodiesterase

Glycerophosphodiester phosphodiesterases (GDPDs; EC 3.1.4.46) typically hydrolyze glycerophosphodiesters to sn-glycerol 3-phosphate (Gro3P) and their corresponding alcohol during patho/physiological processes in bacteria and eukaryotes. GDPD(-like) domains were identified in the structural particle of bacterial viruses (bacteriophages) specifically infecting Gram-positive bacteria. The GDPD of phage 17 (Ld17; GDPD_Ld17), representative of the group b Lactobacillus delbrueckii subsp. bulgaricus (Ldb)-infecting bacteriophages, was shown to hydrolyze, besides the simple glycerophosphodiester, two complex surface-associated carbohydrates of the Ldb17 cell envelope: the Gro3P decoration of the major surface polysaccharide D-galactan and the oligo(glycerol phosphate) backbone of the partially glycosylated cell wall teichoic acid, a minor Ldb17 cell envelope component. Degradation of cell wall teichoic acid occurs according to an exolytic mechanism, and Gro3P substitution is presumed to be inhibitory for GDPD_Ld17 activity. The presence of the GDPD_Ld17 homotrimer in the viral baseplate structure involved in phage-host interaction together with the dependence of native GDPD activity, adsorption, and efficiency of plating of Ca²⁺ ions supports a role for GDPD_Ld17 activity during phage adsorption and/or phage genome injection. In contrast to GDPD_Ld17, we could not identify any enzymatic activity for the GDPD-like domain in the neck passage structure of phage 340, a 936-type Lactococcus lactis subsp. lactis bacteriophage.