Recombinant Escherichia coli Phage shock protein G (pspG)

Introduction to Recombinant Escherichia coli Phage Shock Protein G (PspG)

Recombinant E. coli Phage Shock Protein G (PspG) is a bioengineered version of the native PspG protein, derived from the yjbO gene in E. coli. Originally identified as part of the phage shock protein (Psp) response, PspG is co-regulated with the pspABCDE operon and functions as an effector protein under stress conditions . It is an inner membrane protein critical for maintaining cellular integrity during extracytoplasmic stress, such as filamentous phage infection or protein export defects . Recombinant PspG is typically expressed in E. coli with an N-terminal His-tag for purification and structural studies .

Regulatory Mechanisms

PspG expression is tightly controlled by the PspF-dependent regulon, which includes pspABCDE and pspF . Key regulatory elements include:

• Activators: PspF (enhancer-binding protein) and sigma54-RNA polymerase .

• Repressors: PspA, which binds PspF to inhibit its ATPase activity .

• Stress Triggers: Filamentous phage secretion proteins (e.g., pIV), osmotic shock, ethanol exposure, and heat .

Under stress, PspB and PspC transduce signals to PspA, releasing PspF to activate pspG transcription . PspF specifically regulates pspG and pspABCDE, distinguishing it from other sigma54-dependent systems .

Stress Response and Membrane Stability

PspG works in concert with PspC to modulate membrane integrity during stress. Overexpression of PspG reduces bacterial motility, suggesting a role in regulating membrane dynamics . It interacts directly with PspC and self-associates, forming regulatory complexes .

Protein-Protein Interactions

PspG’s interactions with PspC and PspF highlight its role in the Psp regulatory network .

Transcriptional Profiling

Transcriptional profiling of E. coli under pIV overexpression revealed pspG induction alongside pspABCDE, confirming its role in phage shock responses . Similar regulation occurs in Salmonella enterica serovar Typhimurium .

Regulatory Dynamics

PspF’s ATPase activity is inhibited by PspA under non-stress conditions, preventing pspG transcription. Stress triggers PspB/PspC-mediated release of PspF, enabling sigma54-dependent activation .

Functional Impact

• Motility Defects: Overexpression of PspG reduces motility, suggesting a role in membrane remodeling .

• Cross-Regulation: PspG’s expression is independent of heat shock proteins but overlaps with osmotic/ethanol stress responses .