Conformational change of the haemolymph juvenile‐hormone‐binding protein from Galleria mellonella (L)

Abstract

A juvenile‐hormone‐binding protein (juvenile‐hormone carrier), isolated fromGalleria mellonella haemolymph, was treated with trypsin, chymotrypsin, carboxypeptidase A and subtilisin. Among these enzymes, only subtilisin was able to affect juvenile‐hormone‐binding activity of this protein. With SDS/PAGE it was shown that juvenile‐hormone‐binding protein, a 32‐kDa peptide, is first slowly converted into a 30‐kDa molecule, then into two or three smaller‐molecular‐mass species (20–25 kDa), which in turn were further digested to small peptides undetectable in PAGE. The 30‐kDa peptide has a 2.4‐times‐higher dissociation constant for juvenile hormone than the native protein. No binding activity was detected for 20–25‐kDa peptides. The rate of proteolysis of juvenile‐hormone‐binding protein was decreased by more than twofold in the presence of hormone, however, the overall cleavage pattern was unchanged. Under non‐denaturing conditions, free binding‐protein molecules could be separated from juvenile‐hormone–binding‐protein complex due to a slower electrophoretic mobility of the complex. As judged from ultracentrifugation and cross‐linking experiments, binding of the hormone to its haemolymph carrier does not induce formation of oligomers, but shifts the sedimentation coefficient from 2.30S to 2.71S. It is conclude that juvenile‐hormone binding induces a conformational transition of its carrier protein. This hormone‐induced change might have a physiological significance for signal transmission. Copyright © 1991, Wiley Blackwell. All rights reserved