Scaffolding proteins and their role in viral assembly

Scaffolding proteins are proteins that are required to catalyse, regulate o r modulate some step in the assembly of a macromolecular complex. They asso ciate specifically with the nascent protein complex during assembly, but ar e subsequently removed, and are absent from the mature structure. Scaffoldi ng proteins have been described primarily from viral systems, in particular from the double-stranded DNA bacteriophages, but most likely play a more g eneral role in macromolecular assembly, a fundamental process in all biolog ical systems. Scaffolding proteins may act in a specific fashion, by active ly encouraging the formation of correct protein-protein interactions, or mo re generally by nucleating and promoting assembly. They may also work to en sure the fidelity of the assembly process by preventing the formation of im proper interactions, in many ways similar to the role of molecular chaperon es in protein folding. In viruses, scaffolding proteins are found both in t he form of internal cores and external. bracing, and may form elaborate and complex structures. This review will focus on the viral scaffolding protei ns, for which an increasing amount of structural and functional information has recently become available.