Expression, purification, and crystallization of neisserial outer membrane proteins.

Integral outer membrane proteins (OMPs) play key roles in solute transport, adhesion, and other processes. In Neisseria, they can also function as major protective antigens. Structural, biophysical, and immunological studies of Neisserial OMPs require their isolation in milligram quantities. Purification of any OMP directly from Neisseria would require the growth of large quantities of cell mass, with attendant concerns about safety and convenience. As a result, many investigators have developed methods for expression of OMPs into inclusion bodies in E. coli, followed by refolding of the resolubilized protein. Here we describe such a method, as optimized for the PorA porin but which can be applied, with suitable adaptation, to other OMPs. We also describe an approach to the crystallization of PorA.