The Nuclear Transport Machinery Recognizes Nucleoplasmin-Histone Complexes

作者：Arregi Igor; Falces Jorge; Banuelos Sonia; Urbaneja Maria A; Taneva Stefka G^*

来源：Biochemistry, 2011, 50(33): 7104-7110.

DOI：10.1021/bi2008867

The nuclear transport of the chromatin remodeling protein nucleoplasmin and chromatin building histones is mediated by importins. Nucleoplasmin (NP) contains a classical bipartite nuclear localization signal (NLS) that is recognized by the importin alpha/beta heterodimer, while histones present multiple NLS-like motifs that are recognized by importin beta family members for nuclear targeting. To explore the possibility of a cotransport of histones and their chaperone NP to the nucleus, we have analyzed the assembly of complexes of NP/histones with importins by means of fluorescence anisotropy, centrifugation in sucrose gradients, and isothermal titration calorimetry. Data show that importin alpha Delta IBB (a truncated form of importin alpha lacking the autoinhibitory N-terminal domain) and histones (linker, H5, and nucleosomal core, H2AH2B) can simultaneously bind to NP. Analysis of the binding energetics reveals an enthalpy-driven formation of high affinity ternary, NP/Delta alpha/H5 and NP/Delta alpha/H2AH2B, complexes. We find that different amount of importin alpha molecules can be loaded on NP/histone complexes dependent on the histone type, linker or core, and the amount of bound histones. We further demonstrate that NP/H5 complexes can also incorporate importin alpha/beta thus forming quaternary NP/histones/alpha/beta complexes that might represent a putative coimport pathway for nuclear import of histones and their chaperone protein NP, enhancing the histone import efficiency.

• 出版日期2011-8-23