Retroviral nucleocapsides (shell proteins) often contain zinc centers as structure-determining units. The Zn2+ ions generally connect the protein components by coordination of three cysteine residues and a histidine unit.
The nucleocapsid proteins are found in the shells of intact retroviruses, present with around 1000 copies. This leads to an unusally high zinc concentration (1 mmol/l).
Coordination of the Zn2+ ions by a histidine residue and three cysteine residues
General view of a human influenza virus with microphoto