High resolution structure of Vibrio cholerae acylphosphatase (VcAcP) cage: Identification of drugs, location of its binding site and engineering to facilitate cage formation.

Protein cages have recently emerged as an extraordinary drug-delivery system due to its biocompatibility, biodegradability, low toxicity, ease to manipulate and engineer. We have reported earlier the formation and architecture of a do-decameric cage-like architecture of Vibrio cholerae acylphosphatase (VcAcP) at 3.1 Å. High resolution (2.4 Å) crystal structure of VcAcP cage, reported here, illuminates a potential binding site for sulphate/phosphate containing drugs whereas analysis of its subunit association and interfaces indicates high potential for cage engineering. Tryptophan quenching studies indeed discloses noteworthy binding with various sulphate/phosphate containing nucleotide-based drugs and vitamin B6 (PLP) demonstrating that exterior surface of VcAcP protein cage can be exploited as multifunctional carrier. Moreover, a quadruple mutant L30C/T68C/N40C/L81C-VcAcP (QM-VcAcP) capable to form an intricate disulphide bonded VcAcP cage has been designed. SEC, SDS-PAGE analysis and DLS experiment confirmed cysteine mediated engineered VcAcP cage formation.