Methylthioadenosine deaminase in an alternative quorum sensing pathway in Pseudomonas aeruginosa

Pseudomonas aeruginosa possesses an unusual pathway for 5′-methylthioadenosine (MTA) metabolism involving deamination to 5′-methylthioinosine (MTI) followed by N-ribosyl phosphorolysis to hypoxanthine and 5-methylthio-α-d-ribose 1-phosphate. The specific MTI phosphorylase of P. aeruginosa has been reported [Guan, R., Ho, M. C., Almo, S. C., and Schramm, V. L. (2011) Biochemistry 50, 1247–1254], and here we characterize MTA deaminase from P. aeruginosa (PaMTADA). Genomic analysis indicated the PA3170 locus to be a candidate for MTA deaminase (MTADA). Protein encoded by PA3170 was expressed and shown to deaminate MTA with 40-fold greater catalytic efficiency for MTA than for adenosine. The kcat/Km value of 1.6 × 107 M–1 s–1 for MTA is the highest catalytic efficiency known for an MTA deaminase. 5′-Methylthiocoformycin (MTCF) is a 4.8 pM transition state analogue for PaMTADA but causes no significant inhibition of human adenosine deaminase or MTA phosphorylase. MTCF is permeable to P. aeruginosa and exhibits...