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-phosph ate dehydrogenase (EC 1.2.1.12; GAPDH) as a major protein on the surfa ce of group A streptococci (SDH), which exhibits multiple binding acti vity to various mammalian proteins. We now report that the SDH molecul e also functions as an ADP-ribosylating enzyme, which, in the presence of NAD, is auto-ADP-ribosylated. In a crude cell wall extract of grou p A streptococci, SDH is the only protein that is ADP-ribosylated. SDH found in the streptococcal cytoplasmic fraction could not be ADP-ribo sylated in the presence of NAD. Treatment of ADP-ribosylated SDH with the cytoplasmic fraction removed the ADP-ribose from SDH, suggesting t he presence of an ADP-ribosyl hydrolase in the cytoplasmic compartment . The covalent linkage of ADP-ribose to SDH was stable to neutral hydr oxylamine, sensitive to HgCl2, and inhibitable by free cysteine, indic ating that the modification was at a cysteine residue of SDH. In addit ion to its auto-ADP-ribosylation activity, purified SDH or streptococc al cell wall extracts were able to transfer the ADP-ribose moiety of N AD specifically to free cysteine, resulting in a true thioglycosidic l inkage. 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 man ner. ADP-ribosylation and nitric oxide treatment inhibited the GAPDH a ctivity of SDH. Since ADP-ribosylation and nitric oxide are involved i n signal transduction events, the ADP-ribosylating activity of SDH may enable communication between host and parasite during infection by gr oup A streptococci.