Characterization of methionine export in Corynebacterium glutamicum

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Corynebacterium glutamicum efficiently excretes amino acids, but tight regulation of export systems prevents energy-wasting futile cycles.
• Understanding these regulatory mechanisms is crucial for controlling amino acid flux in microbial systems.

Purpose of the Study:

• To identify genes encoding membrane proteins overexpressed under elevated cytoplasmic methionine conditions.
• To elucidate the role of the BrnFE system in amino acid export, specifically methionine.

Main Methods:

• DNA microarray analysis to identify overexpressed genes.
• Gene deletion, complementation, and overexpression studies of the brnFE genes.
• Amino acid transport assays to determine substrate specificity and rates.

Main Results:

• The brnFE gene, encoding a component of the BrnFE system, was identified as crucial for methionine export.
• BrnFE transports both isoleucine and methionine at similar rates when present in the cytoplasm.
• BrnFE gene expression is induced by cytoplasmic methionine concentration, with methionine being a stronger inducer than isoleucine.
• A second, high-capacity, low-affinity methionine export system exists in C. glutamicum.

Conclusions:

• BrnFE is the dominant methionine export system in Corynebacterium glutamicum under conditions where cytoplasmic methionine does not exceed 50 mM.
• Methionine itself likely acts as the native inducer for the brnFE gene expression.
• The existence of multiple export systems ensures efficient amino acid homeostasis even under high intracellular loads.