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

ABSTRACT Calcium (Ca 2+ ) and phosphate (PO 4 3- ) are fundamental-element and -chemical group in biology. Specifically, the chemistry of both Ca 2+ signalling and phosphorylation switch are independent mechanisms regulating a broad spectrum of biological processes. It is, however, not appreciated that a normal function of phospho-mimic amino acids (aspartate/glutamate) is to interact with Ca 2+ at the atomic level. Here, we leveraged HIV-Ca 2+ biology in primary cells to describe an unknown layer of regulatory processes via Ca 2+ -phosphate (PO 4 3- ) bridge to support protein complex formation. We identified novel HIV phosphorylation sites overlapping Ca 2+ binding domains through phospho-proteomics. Integrating primary cells, molecular virology, structural biology, biophysical and ultrastructural analyses, we presented multiple examples of Ca 2+ -PO 4 3- bridges that support HIV assembly and function. These include Ca 2+ -PO 4 3- bridges: (i) stabilising Pr55 Gag -Pr160 GagPol complex for virus function; (ii) mediating p6 Pol dimerization to support virion maturation; and (iii) modulating viral complex formation to package both viral enzymatic- and cellular-proteins. As the convergent enrichment of these signatured calcium-phosphorylation domains occurs across a wide range of viral and cellular proteins, we propose Ca 2+ -PO 4 3- bridge to be a general principle for Ca 2+ -coordinated phosphorylation switch to regulate biological processes. Full Text Availability The license terms selected by the author(s) for this preprint version do not permit archiving in PMC. The full text is available from the preprint server.