Calcium-phosphate bridge is a novel phosphorylation switch that stabilises protein-complexes during HIV assembly

Area of Science:

• Biochemistry and Molecular Biology
• Virology

Background:

• Calcium (Ca ²⁺ ) and phosphate (PO ₄ ^3- ) are crucial biological elements involved in signaling and phosphorylation.
• The interaction between Ca ²⁺ and phospho-mimic amino acids (aspartate/glutamate) is critical but not fully understood.
• Existing knowledge treats Ca ²⁺ signaling and phosphorylation as independent regulatory mechanisms.

Purpose of the Study:

• To investigate the role of Ca ²⁺ -phosphate (PO ₄ ^3- ) interactions in biological processes, specifically within HIV biology.
• To identify and characterize novel regulatory mechanisms involving Ca ²⁺ and phosphorylation.
• To explore the potential of Ca ²⁺ -PO ₄ ^3- bridges in protein complex formation and viral function.

Main Methods:

• Phospho-proteomics to identify HIV phosphorylation sites overlapping Ca ²⁺ binding domains.
• Integration of primary cell studies, molecular virology, structural biology, and biophysical analyses.
• Ultrastructural analysis to visualize Ca ²⁺ -PO ₄ ^3- bridges.

Main Results:

• Identification of novel Ca ²⁺ -PO ₄ ^3- bridges critical for HIV assembly and function.
• Demonstration of Ca ²⁺ -PO ₄ ^3- bridges stabilizing the Pr55 ^Gag -Pr160 ^GagPol complex.
• Evidence of Ca ²⁺ -PO ₄ ^3- bridges mediating p6 ^Pol dimerization for virion maturation.
• Observation of Ca ²⁺ -PO ₄ ^3- bridges modulating viral complex formation for protein packaging.

Conclusions:

• A novel regulatory mechanism involving Ca ²⁺ -PO ₄ ^3- bridges supports protein complex formation and HIV function.
• Ca ²⁺ -PO ₄ ^3- bridges are essential for stabilizing viral protein complexes and facilitating virion maturation.
• The Ca ²⁺ -PO ₄ ^3- bridge represents a general principle for Ca ²⁺ -coordinated phosphorylation switches in biological regulation across diverse proteins.