Galactosyltransferase, conformation

Ramakrishnan, B. and Qasba, P.K. 2001. Crystal structure of lactose synthase reveals a large conformational change in its catalytic component, the beta-1,4-galactosyltransferase-I. JMol Biol 310(1) 205—218. 

Conformational changes have been observed or suspected for galactosyltransferase. Magee and Ebner (1974) speculated on the occurrence... 

An alternative possibility involves an induced conformational change in a-lactalhumin as a result of complexing with galactosyltransferase, so as to produce an affinity for A -acetyllactosamine. Although this explanation appears never to have heen ruled out, there would be no need to invoke it, since it is already known (Klee and Klee, 1970, 1972 Andrews, 1969 Fitzgerald et al., 1970a) that galactosyltransferase has the innate ability to carry out this reaction, even in the total absence of a-lactalbumin. 

Therefore, the simplest explanation for the action of a-lactalbumin and galactosyltransferase, as suggested by Browne et al. (1969), is that a-lactalbumin, in complexing with galactosyltransferase, modifies the conformational structure of the latter to produce a form of the enzyme that more readily catalyzes the production of lactose, and then does so in preference to A -acetyllactosamine. 

Of the conformational changes that occur in galactosyltransferase, particularly concomitant with the addition of Mn(II), much remains to be learned in correlating structural changes with the onset of enzymatic activity. 

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