Expression and crystallization of several forms of the Propionibacterium shermanii transcarboxylase 5S subunit.

The dimeric outer 5S subunit of transcarboxylase has been expressed in three different forms and crystallized: native 5S, 5S-His(6) and selenomethione-5S-His(6). All the crystals have an orthorhombic space group, but while native 5S forms primitive orthorhombic crystals, 5S-His(6) crystals are either C-centered or primitive and SeMet-5S-His(6) crystals are C-centered. Crystallization of native 5S requires the addition of lithium sulfate, whereas this salt prevented crystallization of 5S-His(6). All 5S crystals diffract to approximately 2.0 A resolution with synchrotron radiation. Efforts are under way to solve the structure of SeMet-5S-His(6) using MAD.