Aminofutalosine Deaminase in the Menaquinone Pathway ofHelicobacter pylori

Helicobacter pyloriis a Gram-negative bacterium that is responsible for gastric and duodenal ulcers.H. pyloriuses the unusualmqnpathway with aminofutalosine (AFL) as an intermediate for menaquinone biosynthesis. Previous reports indicate that hydrolysis of AFL by 5′-methylthioadenosine nucleosidase (HpMTAN) is the direct path for producing downstream metabolites in themqnpathway. However, genomic analysis indicatesjhp0252is a candidate for encoding AFL deaminase (AFLDA), an activity for deaminating aminofutolasine. The product, futalosine, is not a known substrate for bacterial MTANs. Recombinant jhp0252 was expressed and characterized as an AFL deaminase (HpAFLDA). Its catalytic specificity includes AFL, 5′-methylthioadenosine, 5′-deoxyadenosine, adenosine, andS-adenosylhomocysteine. Thek_cat/K_mvalue for AFL is 6.8 × 10⁴M^-1s^-1, 26-fold greater than that for adenosine. 5′-Methylthiocoformycin (MTCF) is a slow-onset inhibitor forHpAFLDA and demonstrated inhibitory effects onH. pylorigrowth. Supplementation with futalosine partially restoredH. pylorigrowth under MTCF treatment, suggesting AFL deamination is significant for cell growth. The crystal structures of apo-HpAFLDA and with MTCF at the catalytic sites show a catalytic site Zn²⁺or Fe²⁺as the water-activating group. With bound MTCF, the metal ion is 2.0 Å from the sp³hydroxyl group of the transition state analogue. Metabolomics analysis revealed thatHpAFLDA has intracellular activity and is inhibited by MTCF. Themqnpathway inH. pyloribifurcates at aminofutalosine withHpMTAN producing adenine and depurinated futalosine andHpAFLDA producing futalosine. Inhibition of cellularHpMTAN orHpAFLDA decreased the cellular content of menaquinone-6, supporting roles for both enzymes in the pathway.