Secretory immunoglobulin a from human milk catalyzes milk protein phosphorylation |
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Authors: | Georgy A Nevinsky Yury Ya Kit Dmitry V Semenov Denis Yu Khumankov Valentina N Buneva |
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Institution: | (1) Siberian Division of Russian Academy of Sciences, Nvosibirsk Institute of Bioorganic Chemistry, Lavrentieva Ave. 8, 630090 Novosibirsk, Russia |
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Abstract: | This article presents evidence that protein kinase activity is an intrin sic property of secretory immunoglobulin A (sIgA)
from milk of healthy human mothers. Polyclonal sIgA was purified by sequential chromatog raphy on protein A-Sepharose, DEAE-cellulose,
and gel filtration on Toyopearl HW-55 and Sepharose 4B columns. Its purity was established by one-and two-dimensional SDS-PAGE.
The protein kinase activity was inhibited by specific antibodies (Abs) against sIgA, and was stable to acidic and alkaline
conditions. Catalytic sIgA showed optimal reaction conditions (pH and MgCl2 concentration) and substrate specificity dif ferent from those of known protein kinases; i.e., sIgA phosphorylated the serine
residues of various milk proteins in the presence of different γ-32P]nucleoside-and deoxynucleoside-5’-triphosphates. The homoge neous Fab fragment of sIgA also showed kinase activity. An ATP-binding
activity of fractions of sIgA was demonstrated by affinity chromatog raphy on ATP-Sepharose and by covalent binding of an
affinity analog of ATP; this activity was mediated by the L chain of sIgA. The authors believe these observations are the
first example of the catalytic activity of IgA Abs and of natural catalytic Abs with synthetic activity. In addition, the
findings suggest the likelihood that catalytic Abs are generated by the immune system of healthy mothers. |
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Keywords: | Catalytic antibodies protein kinases human mother’ s milk |
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