GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE ON THE SURFACE OF GROUP-A STREPTOCOCCI IS ALSO AN ADP-RIBOSYLATING ENZYME

We recently identified an enzymatically active glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12; GAPDH) as a major protein on the surface of group A streptococci (SDH), which exhibits multiple binding activity to various mammalian proteins. We now report that the SDH molecule also functions as an ADP-ribosylating enzyme, which, in the presence of NAD, is auto-ADP-ribosylated. In a crude cell wall extract of group A streptococci, SDH is the only protein that is ADP-ribosylated. SDH found in the streptococcal cytoplasmic fraction could not be ADP-ribosylated in the presence of NAD. Treatment of ADP-ribosylated SDH with the cytoplasmic fraction removed the ADP-ribose from SDH, suggesting the presence of an ADP-ribosyl hydrolase in the cytoplasmic compartment. The covalent linkage of ADP-ribose to SDH was stable to neutral hydroxylamine, sensitive to HgCl2, and inhibitable by free cysteine, indicating that the modification was at a cysteine residue of SDH. In addition to its auto-ADP-ribosylation activity, purified SDH or streptococcal cell wall extracts were able to transfer the ADP-ribose moiety of NAD specifically to free cysteine, resulting in a true thioglycosidic linkage. Treatment of purified SDH or the crude cell wall extract with sodium nitroprusside, which spontaneously generates nitric oxide, was found to stimulate the ADP-ribosylation of SDH in a time-dependent manner. ADP-ribosylation and nitric oxide treatment inhibited the GAPDH activity of SDH. Since ADP-ribosylation and nitric oxide are involved in signal transduction events, the ADP-ribosylating activity of SDH may enable communication between host and parasite during infection by group A streptococci.