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.