A putative alpha-helical porin from Corynebacterium glutamicum

Area of Science:

• Structural biology
• Microbiology
• Biochemistry

Background:

• The cell wall of Corynebacterium glutamicum features a mycolic acid layer, necessitating porins for material transport.
• Porin B (PorB) is a key protein facilitating transport across this barrier.

Purpose of the Study:

• To determine the molecular structure of Porin B (PorB) from Corynebacterium glutamicum.
• To investigate the structural basis for PorB function in the context of the bacterial cell wall.

Main Methods:

• Recombinant PorB production in Escherichia coli.
• Purification, crystallization, and X-ray diffraction analysis of PorB.
• Construction of an oligomeric model based on structural data and functional properties.

Main Results:

• 16 independent molecular structures of PorB were resolved up to 1.8 A resolution.
• A conserved globular core of 70 residues with four alpha-helices was identified.
• Variations were observed in the N- and C-terminal extensions, while crystal packing did not directly support an oligomeric channel.

Conclusions:

• The determined structure of PorB, an alpha-helical porin, is unusual for bacterial outer envelopes, which typically feature beta-barrels.
• A model for the oligomeric structure of native PorB was proposed, consistent with its function and properties.
• The findings are relevant to understanding transport mechanisms in mycolata, including human pathogens.