A metal binding in the polypeptide chain improves the folding efficiency of a denatured and reduced protein.
In order to examine the effect of a metal binding to the polypeptide chain on the aggregation of a protein in the refolding process, we prepared a mutant hen lysozyme possessing the same Ca(2+) binding site as in human alpha-lactalbumin by Escherichia coli expression system (Ser(-1) CaB lysozyme). In the presence of 2 mM CaCl(2), the refolding yield of Ser(-1) CaB lysozyme at a low protein concentration (25 microg/mL) was similar to that of the wild-type lysozyme (80%), but that at high protein concentration (200 microg/mL) decreased (15%) due to aggregation comparing to that of the wild-type lysozyme (45%). However, the refolding yield of Ser(-1) CaB lysozyme in the presence of 100 mM CaCl(2) even at a protein concentration of 200 microg/mL was 80% and was higher than that of the wild-type lysozyme. From analysis of chemical shift changes of the cross peaks in the backbone region of total correlated spectroscopy (TOCSY) spectra of a decapeptide possessing the same calcium binding site as in Ser(-1) CaB lysozyme in the presence of various concentrations of Ca(2+), it was suggested that the dissociation constant of Ca(2+)-peptide complex was estimated to be 20-36 mM. Moreover, the solubility of the denatured Ser(-1) CaB lysozyme in the presence of 100 mM CaCl(2) was higher than that in the presence of 2 mM CaCl(2) whereas the solubility of the denatured Ser(-1) lysozyme in the presence of 100 mM CaCl(2) was not higher than that in the presence of 2 mM CaCl(2). Therefore, it was concluded that the reduced lysozyme possessing the Ca(2+) binding site was efficiently folded in the presence of high concentration of Ca(2+) (100 mM) even at high protein concentration due to depression of aggregation by the binding of Ca(2+) to the polypeptide chain in Ser(-1) CaB lysozyme.
Ohkuri
Takatoshi
T
Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Ueda
Tadashi
T
Yoshida
Yuichiro
Y
Abe
Yoshito
Y
Hamasaki
Naotaka
N
Imoto
Taiji
T
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002645:Chickens; D007768:Lactalbumin; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism; D015202:Protein Engineering; D017510:Protein Folding; D020673:Protein Renaturation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism
D011993:Recombinant Fusion Proteins; D007768:Lactalbumin; D009113:Muramidase; D002118:Calcium