Novel functional insights into a modified sugar-binding protein from Synechococcus MITS9220

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Photoautotrophic marine picocyanobacteria are increasingly recognized for diverse metabolic strategies.
• Genomic data suggest picocyanobacteria assimilate organic nutrients via ATP-binding cassette importers, involving substrate-binding proteins.
• Understanding these nutrient assimilation pathways is crucial for deciphering picocyanobacterial ecology.

Purpose of the Study:

• To functionally characterize a modified sugar-binding protein (MsBP) from marine Synechococcus MITS9220.
• To investigate the ligand-binding properties and structural basis of MsBP function.
• To explore novel molecular variations in sugar-binding protein scaffolds and their implications for picocyanobacterial metabolism.

Main Methods:

• Ligand screening of MsBP to determine binding affinities for various molecules.
• X-ray crystallography to obtain structures of apo MsBP and zinc-bound MsBP (Zn-MsBP).
• Structural analysis to identify key residues and conformational changes upon zinc binding.

Main Results:

• MsBP exhibits specific affinity for zinc (K_D ~ 1.3 μM) and phosphate-modified sugars in the presence of zinc (K_D ~ 5.8 μM).
• Zinc binding induces structural changes in MsBP, leading to a partially-closed substrate-binding cavity.
• Crystal structures reveal a positively charged binding cleft and sequestration of sulfate ions mimicking phosphate-modified sugars.

Conclusions:

• The characterized MsBP represents a novel variation of the sugar-binding protein scaffold.
• Findings support a mixotrophic strategy in marine picocyanobacteria, involving the acquisition of organic nutrients.
• This study advances our understanding of metabolic flexibility in ubiquitous photosynthetic bacteria.