4tnm | pdb_00004tnm
Crystal structure of Arabidopsis importin-alpha3 armadillo repeat domain
Structural highlights
FunctionIMPA3_ARATH Binds to conventional NLS motifs and mediates nuclear protein import across the nuclear envelope (By similarity). Acts as cellular receptor for the nuclear import of the virD2 protein of Agrobacterium, but is not essential for Agrobacterium-mediated root transformation (PubMed:18836040). May be involved in the regulation of pathogen-induced salicylic acid accumulation (PubMed:15964279).[UniProtKB:Q96321][1] [2] Publication Abstract from PubMedImportin-alphas are essential adapter proteins that recruit cytoplasmic proteins destined for active nuclear import to the nuclear transport machinery. Cargo proteins interact with the importin-alpha armadillo repeat domain via nuclear localization sequences (NLSs), short amino acids motifs enriched in Lys and Arg residues. Plant genomes typically encode several importin-alpha paralogs that can have both specific and partially redundant functions. Although some cargos are preferentially imported by a distinct importin-alpha, it remains unknown how this specificity is generated and to what extent cargos compete for binding to nuclear transport receptors. Here we report that the effector protein HaRxL106 from the oomycete pathogen Hyaloperonospora arabidopsidis co-opts the host cell's nuclear import machinery. We use HaRxL106 as a probe to determine redundant and specific functions of importin-alpha paralogs from Arabidopsis thaliana. A crystal structure of the importin-alpha3/MOS6 armadillo repeat domain suggests that five of the six Arabidopsis importin-alphas expressed in rosette leaves have an almost identical NLS binding site. Comparison of the importin-alpha binding affinities of HaRxL106 and other cargos in vitro and in plant cells suggests that relatively small affinity differences in vitro affect the rate of transport complex formation in vivo. Our results suggest that cargo affinity for importin-alpha, sequence variation at the importin-alpha NLS binding sites and tissue-specific expression levels of importin-alphas determine formation of cargo/importin-alpha transport complexes in plant cells. This article is protected by copyright. All rights reserved. Probing formation of cargo/importin-alpha transport complexes in plant cells using a pathogen effector.,Wirthmueller L, Roth C, Fabro G, Caillaud MC, Rallapalli G, Asai S, Sklenar J, Jones AM, Wiermer M, Jones JD, Banfield MJ Plant J. 2014 Oct 6. doi: 10.1111/tpj.12691. PMID:25284001[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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