Leucine-rich-repeat-containing variable lymphocyte receptors as modules to target plant-expressed proteins.

BACKGROUND

The ability to target and manipulate protein-based cellular processes would accelerate plant research; yet, the technology to specifically and selectively target plant-expressed proteins is still in its infancy. Leucine-rich repeats (LRRs) are ubiquitously present protein domains involved in mediating protein-protein interactions. LRRs confer the binding specificity to the highly diverse variable lymphocyte receptor (VLR) antibodies (including VLRA, VLRB and VLRC types) that jawless vertebrates make as the functional equivalents of jawed vertebrate immunoglobulin-based antibodies.

RESULTS

In this study, VLRBs targeting an effector protein from a plant pathogen, HopM1, were developed by immunizing lampreys and using yeast surface display to select for high-affinity VLRBs. HopM1-specific VLRBs (VLR) were expressed in the cytosol, the -Golgi network, and the apoplast. Expression of VLR was higher when the protein localized to an oxidizing environment that would favor disulfide bridge formation (when VLR was not localized to the cytoplasm), as disulfide bonds are necessary for proper VLR folding. VLR specifically interacted with HopM1 but not with an unrelated bacterial effector protein while HopM1 failed to interact with a non-specific VLRB.

CONCLUSIONS

In the future, VLRs may be used as flexible modules to bind proteins or carbohydrates of interest , with broad possibilities for their use by binding directly to their targets and inhibiting their action, or by creating chimeric proteins with new specificities in which endogenous LRR domains are replaced by those present in VLRs.