Complex assembly behavior during the encapsulation of green fluorescent protein analogs in virus derived protein capsules

Enzymes encapsulated in nanocontainers are a better model of the conditions inside a living cell than free enzymes in solution. In a first step toward the encapsulation of multiple enzymes inside the cowpea chlorotic mottle virus (CCMV) capsid, enhanced green fluorescent protein (EGFP) was attached to CCMV capsid proteins. The capsid protein–EGFP complex was then co-assembled with wild-type capsid protein (wt CP) in various ratios. At higher complex to wt CP ratios, the number of EGFP per capsid decreased instead of leveling off. We propose that this unexpected behavior is caused by pH-induced disassembly of the capsid protein–EGFP complex as well as by concentration and ratio dependent dimerization of the complex, making it partially unavailable for incorporation into the capsid.