Membrane simulations of OpcA: gating in the loops?

Mobility of extracellular loops may play an important role in the function of outer membrane proteins from Gram-negative bacteria. Molecular dynamics simulations of OpcA from Neisseria meningitidis, embedded in a lipid bilayer, have been used to explore the relationship between the crystal structure and dynamic function of this protein. The results suggest that the crystal environment may constrain the membrane protein structure in a nonphysiological state. The presence of lipids and physiological salt concentrations result in changes in the conformation of the extracellular loops of OpcA, leading to opening of a pore, and to modulation of the molecular surface implicated in recognition of proteoglycan. These changes may be related to the role of OpcA in pathogenesis via modulation of the conformation of a possible sialic acid binding site.