Interaction of tear lipocalin with lysozyme and lactoferrin

The interaction of human tear lipocalin with lysozyme and lactoferrin was s tudied by electron paramagnetic resonance (EPR) spectroscopy. TL mutants I9 8C and F99C were spin labeled with MTSL and its derivative. The spectra dem onstrated that at sites C98 and C99 the mobility of the nitroxides was redu ced in the presence of lysozyme, lactoferrin, but not albumin. The reduced mobility was manifested as a reduction in side chain motion and backbone fl uctuations. The overall correlation time of tear lipocalin, measured by MTS L derivative-labeled F99C, was prolonged in the presence of lysozyme and la ctoferrin indicating that the interaction involves direct contact. The effe ct was mitigated at high salt concentration suggesting an electrostatic int eraction of the molecules. The reduction in side chain mobility at C98 and C99 of tear lipocalin was observed in tears. Taken together, the data indic ate that tear lipocalin interacts with both lysozyme and lactoferrin and su ggest that they may function in concert with one another. (C) 1999 Academic Press.