Hydrogen-exchange kinetics of reduced alpha-lactalbumin bound to the chaperonin GroEL

alpha-Lactalbumin in which all the disulfide bonds are fully reduced (RLA) is known to bind strongly to the chaperonin GroEL, Although RLA is more unfolded than the native state and the molten globule state of alpha-lactalbumin, the CD spectrum of RLA in the far-UV region shows that RLA is not fully unfolded but has an appreciable amount of secondary structure, To investigate whether the secondary structure elements present in RLA are responsible for the recognition of RLA by GroEL or not, we have examined the hydrogen-exchange kinetics of RLA in the presence and absence of GroEL, Our results show that the hydrogen-exchange kinetics of RLA bound to GroEL is identical to that of free RLA, This implies that the secondary structure elements in RLA are not important for the recognition by GroEL, but the unstructured parts of RLA that are not relevant to the stability of the secondary structure provide strong recognition sites of RLA.