Crystal structure of a phosphorylation-coupled saccharide transporter

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Saccharides are vital for nutrition across all life forms.
• Bacterial phosphoenolpyruvate-dependent phosphotransferase systems (PTS) are unique saccharide uptake and phosphorylation mechanisms.
• EIIC proteins are integral membrane components of the bacterial PTS.

Purpose of the Study:

• To determine the crystal structure of a diacetylchitobiose-transporting EIIC from Bacillus cereus.
• To elucidate the structural basis for substrate binding and phosphorylation within the EIIC transporter.
• To provide insights into the mechanism of sugar translocation in bacteria.

Main Methods:

• X-ray crystallography was employed to obtain the high-resolution structure of the EIIC.
• Structural analysis focused on the homodimeric architecture and substrate-binding pocket.
• Identification of conserved residues involved in substrate interaction and phosphorylation.

Main Results:

• The EIIC functions as a homodimer with a significant interface between amino-terminal domains.
• Each protomer possesses a carboxy-terminal binding pocket accommodating diacetylchitobiose.
• The substrate-binding site is occluded from both membrane faces, with phosphorylation sites near His250 and Glu334.

Conclusions:

• The determined structure reveals the architecture of bacterial EIIC transporters.
• Key determinants for diacetylchitobiose binding and phosphorylation have been identified.
• This structural framework aids in understanding the mechanism of sugar translocation via PTS.