Bacterial microcompartments are typically enclosed by a self-assembling shell formed by many copies of just a few proteins. The shell is icosahedral, consisting of hexameric units packed into flat planes, which are joined together by pentamers at the vertices. You can see this arrangement in this shell structure of a microcompartment called an encapsulin that Thermotoga maritima use to sequester soluble iron so that it does not react with reactive oxygen species and damage the cell .
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