NADP and NAD utilization in Haemophilus influenzae

Exogenous NAD utilization or pyridine nucleotide cycle metabolism is used b y many bacteria to maintain NAD turnover and to limit energy-dependent de n ovo NAD synthesis. The genus Haemophilus includes several important pathoge nic bacterial species that require NAD as an essential growth factor. The m olecular mechanisms of NAD uptake and processing are understood only in par t for Haemophilus. In this report, we present data showing that the outer m embrane lipoprotein e(P4), encoded by the hel gene, and an exported 5'-nucl eotidase (HI0206), assigned as nadN, are necessary for NAD and NADP utiliza tion. Lipoprotein e(P4) is characterized as an acid phosphatase that uses N ADP as substrate. Its phosphatase activity is inhibited by compounds such a s adenosine or NMN. The nadN gene product was characterized as an NAD-nucle otidase, responsible for the hydrolysis of NAD. H. influenzae hel and nadN mutants had defined growth deficiencies. For growth, the uptake and process ing of the essential cofactors NADP and NAD required e(P4) and 5'-nucleotid ase. In addition, adenosine was identified as a potent growth inhibitor of wild-type H. influenzae strains, when NADP was used as the sole source of n icotinamide-ribosyl.