J. Biol. Chem., Vol. 265, Issue 13, 7268-7272, May, 1990
NMR and ESR studies on human pregnancy zone protein. Comparison with human alpha 2-macroglobulin
P Gettins and L Sottrup-Jensen
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
NMR and ESR spectroscopies have been used to examine the plasma protease
inhibitor pregnancy zone protein (PZP) and its complex with chymotrypsin.
The 1H NMR spectrum of PZP shows relatively few sharp resonances, which, by
analogy with human alpha 2-macroglobulin, probably arise from the
proteolytically sensitive bait region. Upon reaction with chymotrypsin to
form a 1:1 protease.PZP tetramer complex, there is a large increase in the
intensity of sharp resonances due to an increase in mobility of these
residues. 35Cl NMR has been used to follow binding of zinc and manganese to
apo-PZP. Zinc binding causes a linear broadening of the bulk Cl-,
consistent with access of Cl- to PZP- bound zinc. Since zinc in the two
highest affinity sites in human alpha 2-macroglobulin causes no broadening
of Cl-, it is concluded that these zinc sites are absent from PZP. The
mobility of chymotrypsin in the PZP.chymotrypsin complex was examined by
covalently attaching a nitroxide spin label at the serine residue in the
active site of the enzyme and examining the appearance of the ESR spectrum.
The chymotrypsin is rigidly held by the PZP to which it is covalently
bound. In an analogous experiment performed previously on alpha 2-
macroglobulin, chymotrypsin, bound in the presence of methylamine and
therefore largely noncovalently bound, was found to be free to rotate
inside the cage formed by the protease inhibitor.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?