PhoH2 proteins couple RNA helicase and RNAse activities

Abstract

PhoH2 proteins are found in a very diverse range of microorganisms that span bacteria and archaea. These proteins are composed of two domains: an N‐terminal PIN‐domain fused with a C‐terminal PhoH domain. Collectively this fusion functions as an RNA helicase and ribonuclease. In other genomic contexts, PINdomains and PhoHdomains are separate but adjacent suggesting association to achieve similar function. Exclusively among the mycobacteria, PhoH2 proteins are encoded in the genome with an upstream gene, phoAT, which is thought to play the role of an antitoxin (in place of the traditional VapB antitoxin that lies upstream of the 47 other PINdomains in the mycobacterial genome). This review examines PhoH2 proteins as a whole and describes the bioinformatics, biochemical, structural, and biological properties of the two domains that make up PhoH2: PIN and PhoH. We review the transcriptional regulators of phoH2 from two mycobacterial species and speculate on the function of PhoH2 proteins in the context of a Type II toxin–antitoxin system which are thought to play a role in the stress response in bacteria.

Post-transcriptional modulation of the SigF regulon in Mycobacterium smegmatis by the PhoH2 toxin-antitoxin

“…(C) Upon relief of stress, we predict that the expression of anti-sigma factor antagonists decreases, enabling RsbW proteins to remain bound to SigF, sequestering its activity until further stress conditions are met. Four major stem-loop secondary structures taken from the predicted secondary structure of sigF RNA and (B) predicted secondary structure of 5'5 RNA and the preferred target sequence [11]. The stem loops are coloured by base pair probability and the preferred target sequences are highlighted with black circles and white text.…”

“…[G/C] [10]. This suggests that PhoH2, similar to other PIN-domain containing proteins [12], is a toxin-antitoxin with additional RNA helicase activity that acts on specific RNA substrates and is likely to play a role in the adaptive response to changing environmental conditions [10,11].…”

“…PhoH2 is a modular enzyme with a PIN-domain RNAse fused with a PhoH-domain RNA helicase [10,11]. In mycobacteria, PhoH2 is co-transcribed with a short, upstream gene, phoAT, whose protein product interacts with PhoH2 [10].…”

Post-transcriptional modulation of the SigF regulon in Mycobacterium smegmatis by the PhoH2 toxin-antitoxin

“…PhoH2 is a modular enzyme with a PIN-domain RNAse fused with a PhoH-domain RNA helicase [12,13]. In mycobacteria, PhoH2 is co-transcribed with a short, upstream gene, phoAT, whose protein product interacts with PhoH2 [12].…”

“…smegmatis has sequence-specific RNAse and ATP-dependent helicase activities, with preference for double-stranded RNA that contains a 5’-3’ overhang, and where the terminal combination of RNA bases is 5’- A C [A/U] [A/U] [G/C] [ 12 ]. This suggests that PhoH2, similar to other PIN-domain containing proteins [ 14 ], is a toxin-antitoxin with additional RNA helicase activity that acts on specific RNA substrates and is likely to play a role in the adaptive response to changing environmental conditions [ 12 , 13 ].…”