Jensen PE, Gunnarsson M, Stigbrand T. Conformational state and receptor recognition of the C-terminal domain of human alpha(2)-macroglobulin after dissociation into half-molecules.
Clin Chim Acta 2001;
310:157-63. [PMID:
11498081 DOI:
10.1016/s0009-8981(01)00572-1]
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Abstract
BACKGROUND
Dissociation of native human alpha(2)-macroglobulin (alpha(2)M) by sodium thiocyanate generates stable half-molecules with intact thiol esters. Significant conformational changes occur by the dissociation, which are similar to those occurring by transformation from native to methylamine-treated alpha(2)-macroglobulin.
METHODS
The conformational state of the receptor-binding domain of the half-molecules was investigated by receptor binding and clearance studies, and by use of a panel of 11 monoclonal antibodies (mAbs) specific for the 18-kDa C-terminal receptor-binding fragment of alpha(2)-macroglobulin.
RESULTS
The half-molecules simultaneously express epitopes specific for native, as well as epitopes specific for transformed alpha(2)-macroglobulin. While it is possible to immunochemically discriminate between the different forms of tetrameric protein, the half-molecules retain a conformational state with no observed conformational changes in the C-terminal domain following cleavage of thiol esters or bait regions. The in vivo clearance rate in mice was consequently significantly slower for the half-molecules than for the tetrameric receptor-recognized forms of alpha(2)-macroglobulin. Furthermore, half-molecules demonstrate lower affinity for binding to mouse macrophages than methylamine-treated tetrameric alpha(2)-macroglobulin in competition studies.
CONCLUSIONS
It is suggested that contact zones are functionally important for mediating conformational switches, which result in trapping and exposure of the receptor-binding sites.
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