You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

A Two-State Cooperative Expansion Converts the Procapsid Shell of Bacteriophage T5 into a Highly Stable Capsid Isomorphous to the Final Virion Head. Capsids of double-stranded DNA (dsDNA) bacteriophages initially assemble into compact procapsids, which undergo expansion upon the genome packaging. This shell remodeling results from a structural rearrangement of head protein subunits. It is a critical step in the capsid maturation pathway that yields final particles capable to withstand the huge internal pressure generated by the packed DNA. Here, we report on the expansion process of the large capsid (T=13) of bacteriophage T5. We purified the intermediate prohead II form, which is competent for packaging the 121-kbp dsDNA genome, and we investigated its morphology and dimensions using cryo-electron microscopy and small-angle X-ray scattering. Decreasing the pH or the ionic strength triggers expansion of prohead II, converting them into thinner and more faceted capsids isomorphous to the mature virion particles. At low pH, prohead II expansion is a highly cooperative process lacking any detectable intermediate. This two-state reorganization of the capsid lattice per se leads to a remarkable stabilization of the particle. The melting temperature of expanded T5 capsid is virtually identical with that of more complex shells that are reinforced by inter-subunit cross-linking (HK97) or by additional cementing proteins (T4). The T5 capsid with its "simple" two-state conversion thus appears to be a very attractive model for investigating the mechanism of the large-scale allosteric transition that takes place upon the genome packaging of dsDNA bacteriophages.
{"Chemical": []}