Protein Engineering, Design and Selection vol. 17 no. 1 pp. 85-93, 2004
© 2004 Oxford University Press
Fusion of the antiferritin antibody VL domain to barnase results in enhanced solubility and altered pH stability
1Institute of Bio-Organic Chemistry, National Academy of Sciences of Belarus, 2200141, Minsk, Belarus, 3Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry and Institute of Gene Biology, Russian Academy of Sciences, Moscow 117871, Russia and 4Dipartimento ‘Materno Infantile e Tecnologie Biomediche’, Università di Brescia, Brescia 25123, Italy
2 To whom correspondence should be addressed. e-mail: martsev{at}iboch.bas-net.by
Chimeric immunotoxins that combine antigen recognition domains of antibodies and cytotoxic RNases have attracted much attention in recent years as potential targeted agents for cancer immunotherapy. In an attempt to obtain a structurally minimized immunofusion for folding/stability studies, we constructed the chimeric protein VL–barnase. The chimera comprises a small cytotoxic enzyme barnase, ribonuclease from Bacillus amyloliquefaciens, fused to the C-terminus of the light chain variable domain (VL) of the anti-human ferritin monoclonal antibody F11. While the individual VL domain was expressed in Escherichia coli as insoluble protein packed into inclusion bodies, its fusion to barnase resulted in a significant (
70%) fraction of soluble protein, with only a minor insoluble fraction (30%) packed into inclusion bodies. The in vivo solubilizing effect of barnase was also observed in vitro and suggests a chaperone-like role that barnase exerted with regard to the N-terminal VL domain. Cytoplasmic VL–barnase was analyzed for structural and functional properties. The dimeric state of the chimeric protein was demonstrated by size-exclusion chromatography, thus indicating that fusion to barnase did not abrogate the intrinsic dimerization propensity of the VL domain. Ferritin-binding affinity and specificity in terms of constants of association with isoferritins were identical for the isolated VL domain and its barnase fusion, and RNase activity remained unchanged after the fusion. Intrinsic fluorescence spectra showed a fully compact tertiary structure of the fusion protein. However, significantly altered pH stability of the fusion protein versus individual VL and barnase was shown by the pH-induced changes in both intrinsic fluorescence and binding of ANS. Together, the results indicate that VL–barnase retained the antigen-binding affinity, specificity and RNase activity pertinent to the two individual constituents, and that their fusion into a single-chain chimeric protein resulted in an altered tertiary fold and pH stability.
Received August 21, 2003; revised October 23, 2003; accepted October 27, 2003 Edited by Greg Winter
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  Y. Tsybovsky, D. V. Shubenok, Z. I. Kravchuk, and S. P. Martsev Folding of an antibody variable domain in two functional conformations in vitro: calorimetric and spectroscopic study of the anti-ferritin antibody VL domain Protein Eng. Des. Sel., October 24, 2007; (2007) gzm034v1. [Abstract] [Full Text] [PDF]
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