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Llama-Derived Single-Chain Antibody Fragments Directed to Rotavirus VP6 Protein Possess Broad Neutralizing Activity In Vitro and Confer Protection against Diarrhea in Mice▿
Journal of Virology
Group A rotavirus is one of the most common causes of severe diarrhea in human infants and newborn animals. Rotavirus virions are triple-layered particles. The outer capsid proteins VP4 and VP7 are highly variable and represent the major neutralizing antigens. The inner capsid protein VP6 is conserved among group A rotaviruses, is highly immunogenic, and is the target antigen of most immunodiagnosis tests. Llama-derived single-chain antibody fragments (VHH) are the smallest molecules with antigen-binding capacity and can therefore be expected to have properties different from conventional antibodies. In this study a library containing the VHH genes of a llama immunized with recombinant inner capsid protein VP6 was generated. Binders directed to VP6, in its native conformation within the viral particle, were selected and characterized. Four selected VHH directed to conformational epitopes of VP6 recognized all human and animal rotavirus strains tested and could be engineered for their use in immunodiagnostic tests for group A rotavirus detection. Three of the four VHH neutralized rotavirus in vivo independently of the strain serotype. Furthermore, this result was confirmed by in vivo partial protection against rotavirus challenge in a neonatal mouse model. The present study demonstrates for the first time a broad neutralization activity of VP6 specific VHH in vitro and in vivo. Neutralizing VHH directed to VP6 promise to become an essential tool for the prevention and treatment of rotavirus diarrhea.
Phosphorylation by Cdk1 Increases the Binding of Eg5 to Microtubules In Vitro and in Xenopus Egg Extract Spindles
Motor proteins from the kinesin-5 subfamily play an essential role in spindle assembly during cell division of most organisms. These motors crosslink and slide microtubules in the spindle. Kinesin-5 motors are phosphorylated at a conserved site by Cyclin-dependent kinase 1 (Cdk1) during mitosis. Xenopus laevis kinesin-5 has also been reported to be phosphorylated by Aurora A in vitro.
We investigate here the effect of these phosphorylations on kinesin-5 from Xenopus laevis, called Eg5. We find that phosphorylation at threonine 937 in the C-terminal tail of Eg5 by Cdk1 does not affect the velocity of Eg5, but strongly increases its binding to microtubules assembled in buffer. Likewise, this phosphorylation promotes binding of Eg5 to microtubules in Xenopus egg extract spindles. This enhancement of binding elevates the amount of Eg5 in spindles above a critical level required for bipolar spindle formation. We find furthermore that phosphorylation of Xenopus laevis Eg5 by Aurora A at serine 543 in the stalk is not required for spindle formation.
These results show that phosphorylation of Eg5 by Cdk1 has a direct effect on the interaction of this motor with microtubules. In egg extract, phosphorylation of Eg5 by Cdk1 ensures that the amount of Eg5 in the spindle is above a level that is required for spindle formation. This enhanced targeting to the spindle appears therefore to be, at least in part, a direct consequence of the enhanced binding of Eg5 to microtubules upon phosphorylation by Cdk1. These findings advance our understanding of the regulation of this essential mitotic motor protein.
Heating as a rapid purification method for recovering correctly-folded thermotolerant VH and VHH domains
de Marco, Ario
Recombinant antibodies from Camelidae (VHHs) are potentially useful tools for both basic research and biotechnological applications because of their small size, robustness, easy handling and possibility to refold after chemio-physical denaturation. Their heat tolerance is a particularly interesting feature because it has been recently related to both high yields during recombinant expression and selective purification of folded protein.
Purification of recombinant RE3 VHH by heat treatment yielded the same amount of antibody as purification by affinity chromatography and negligible differences were found in stability, secondary structure and functionality. Similar results were obtained using another class of thermotolerant proteins, the single domain VH scaffold, described by Jespers et al. . However, thermosensitive VHs could not withstand the heat treatment and co-precipitated with the bacterial proteins. In both cases, the thermotolerant proteins unfolded during the treatment but promptly refolded when moved back to a compatible temperature.
Heat treatment can simplify the purification protocol of thermotolerant proteins as well as remove any soluble aggregate. Since the re-folding capability after heat-induced denaturation was previously correlated to higher performance during recombinant expression, a unique heating step can be envisaged to screen constructs that can provide high yields of correctly-folded proteins.
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