The structure of the PII-ATP complex.

Area of Science:

• Bacterial signal transduction
• Protein structure and function

Background:

• PII protein regulates glutamine synthetase activity and gene transcription in bacteria.
• Understanding PII structure is crucial for bacterial physiology.

Purpose of the Study:

• To determine the structure of the PII protein in complex with ATP.
• To compare ATP-bound PII structures with previously determined forms.
• To investigate structural differences between PII and its homolog GlnK.

Main Methods:

• X-ray crystallography of PII with ATP using two crystal forms (forms II and III).
• Structural comparison of ATP-bound PII with apo-PII (form I).
• Modeling of PII/GlnK heterotrimers.

Main Results:

• The ATP-bound PII structures reveal a disordered recognition loop and altered C termini compared to apo-PII.
• Structural differences were observed in ATP phosphate interactions between PII and GlnK.
• Models suggest sequence variations at position 82 contribute to functional differences.

Conclusions:

• ATP binding induces significant conformational changes in the PII protein.
• Structural disparities between PII and GlnK, particularly in phosphate binding, explain functional divergence.
• PII and GlnK form heterotrimers, with structural insights into their subunit interactions.