Hfq variant with altered RNA binding functions

Area of Science:

• Molecular Biology
• Microbial Genetics

Background:

• The Hfq protein is a crucial regulator of gene expression through its interaction with RNA molecules.
• Hfq's RNA-binding capacity is essential for various cellular processes, including stress response and growth.

Purpose of the Study:

• To investigate the functional consequences of a specific missense mutation (V43R) in the Hfq protein.
• To elucidate the role of Hfq's RNA-binding activity in poly(A) tail elongation and gene regulation.

Main Methods:

• Site-directed mutagenesis was used to create the Hfq V43R variant.
• In vitro assays assessed RNA binding and poly(A) tail elongation.
• In vivo studies evaluated gene expression (rpoS-lacZ) and growth rates in mutant strains.
• Molecular dynamics simulations were performed to analyze structural changes.

Main Results:

• The Hfq V43R mutation significantly reduced RNA binding and the stimulation of poly(A) tail elongation.
• Overexpression of Hfq V43R did not rescue the growth defect in hfq null mutants and failed to stimulate rpoS-lacZ expression.
• Cells with the hfqV43R allele showed an intermediate phenotype, with derepressed Hfq synthesis but preserved repression of OppA synthesis.
• Molecular dynamics suggested the V43R substitution affects RNA interaction residues (K56, Y55) without altering protein folding or oligomerization.

Conclusions:

• The V43R mutation disrupts critical Hfq functions, particularly RNA binding and associated regulatory activities.
• The V43R variant exhibits dominant-negative effects, indicating that mixed hexamers are non-functional.
• Hfq's role in gene regulation is complex, with specific residues mediating distinct interactions.