KINETIC TRAPS IN LYSOZYME FOLDING

Folding of lysozyme from hen egg white was investigated by using inter rupted refolding experiments. This method makes use of a high energy b arrier between the native state and transient folding intermediates, a nd, in contrast to conventional optical techniques, it enables one to specifically monitor the amount of native molecules during protein fol ding. The results show that under strongly native conditions lysozyme can refold on parallel pathways. The major part of the lysozyme molecu les (86%) refold on a slow kinetic pathway with well-populated partial ly folded states. Additionally, 14% of the molecules fold faster. The rate constant of formation of native molecules on the fast pathway cor responds well to the rate constant expected for folding to occur by a two-state process without any detectable intermediates. The results su ggest that formation of the native state for the major fraction of lys ozyme molecules is retarded compared with the direct folding process. Partially structured intermediates that transiently populate seem to b e kinetically trapped in a conformation that can only slowly reach the native structure.